ZIP codes and county lines in Iowa

472 of the 972 ZIP code areas in Iowa, or 48.6%, overlap more than one county. If your territories, tax rules or service areas are set by county and your list is by ZIP, these are the rows where the two disagree.

ZIP code areas: 972
In more than one county: 472
At least 5% in a second county: 382
Cross a state line: 10

How Iowa compares

Iowa ranks 8 of 52 (the 50 states, DC and Puerto Rico) by the share of its ZIP code areas that overlap more than one county. 99 of its counties have at least one split ZIP code area along an edge. 10 of its ZIP code areas also reach into Minnesota, Missouri, Nebraska and South Dakota, so a ZIP list that is meant to stop at the state line does not.

Counties with the most split ZIP code areas

Polk County: 21 ZIP codes shared with another county
Dallas County: 18 ZIP codes shared with another county
Boone County: 16 ZIP codes shared with another county
Fayette County: 16 ZIP codes shared with another county
Guthrie County: 16 ZIP codes shared with another county

Every split ZIP code area in Iowa

Each row is one ZCTA and the counties its land falls in, largest share first. Counties in another state are marked with that state. Sort by the share outside the main county to put the most evenly divided ones first.

	Share of land by county
50002	Guthrie County 53.4% Adair County 45.2% Audubon County 1.4%	46.6%	3
50006	Hardin County 68.8% Franklin County 30.3% Hamilton County 0.9%	31.2%	3
50014	Story County 56.2% Boone County 43.8%	43.8%	2
50020	Cass County 77.5% Adair County 11.7% Audubon County 9.8% Guthrie County 1.0%	22.5%	4
50022	Cass County 89.3% Audubon County 6.6% Shelby County 4.1%	10.7%	3
50025	Audubon County 98.5% Guthrie County 1.5%	1.5%	2
50026	Guthrie County 57.1% Greene County 42.9%	42.9%	2
50027	Mahaska County 99.3% Poweshiek County 0.8%	0.8%	2
50028	Jasper County 95.5% Marshall County 4.5%	4.5%	2
50029	Guthrie County 92.2% Greene County 7.8%	7.8%	2
50034	Hamilton County 66.8% Wright County 33.2%	33.2%	2
50036	Boone County 98.4% Hamilton County 1.6%	1.6%	2
50039	Dallas County 94.0% Boone County 6.0%	6.0%	2
50042	Audubon County 97.6% Cass County 2.4%	2.4%	2
50044	Marion County 59.4% Mahaska County 36.5% Monroe County 4.1%	40.6%	3
50046	Story County 72.8% Polk County 27.2%	27.2%	2
50047	Warren County 75.6% Polk County 24.4%	24.4%	2
50048	Guthrie County 55.9% Adair County 44.1%	44.1%	2
50049	Lucas County 97.4% Wayne County 1.7% Marion County 0.9%	2.6%	3
50050	Greene County 93.6% Calhoun County 3.9% Carroll County 2.6%	6.4%	3
50055	Story County 65.1% Jasper County 30.5% Marshall County 4.4%	34.9%	3
50058	Guthrie County 39.4% Carroll County 39.0% Audubon County 12.1% Greene County 9.5%	60.6%	4
50061	Madison County 52.2% Warren County 34.0% Dallas County 7.1% Polk County 6.8%	47.8%	4
50064	Greene County 89.4% Boone County 10.6%	10.6%	2
50068	Lucas County 90.9% Wayne County 9.1%	9.1%	2
50070	Madison County 40.0% Adair County 28.3% Dallas County 15.9% Guthrie County 15.9%	60.0%	4
50071	Wright County 55.9% Franklin County 44.1%	44.1%	2
50072	Madison County 74.8% Dallas County 25.2%	25.2%	2
50074	Ringgold County 84.9% Union County 15.1%	15.1%	2
50076	Audubon County 99.1% Guthrie County 0.9%	0.9%	2
50104	Keokuk County 64.4% Poweshiek County 26.0% Mahaska County 9.6%	35.6%	3
50106	Marshall County 51.1% Jasper County 23.3% Tama County 20.3% Poweshiek County 5.4%	48.9%	4
50107	Greene County 88.1% Boone County 11.9%	11.9%	2
50108	Decatur County 88.3% Clarke County 11.7%	11.7%	2
50109	Polk County 53.1% Dallas County 46.9%	46.9%	2
50111	Polk County 66.1% Dallas County 33.9%	33.9%	2
50112	Poweshiek County 74.1% Jasper County 25.9%	25.9%	2
50123	Wayne County 79.5% Lucas County 11.2% Decatur County 6.9% Clarke County 2.4%	20.5%	4
50124	Story County 74.0% Polk County 26.0%	26.0%	2
50126	Hardin County 74.4% Franklin County 25.6%	25.6%	2
50128	Guthrie County 48.6% Greene County 38.9% Dallas County 12.5%	51.4%	3
50129	Greene County 99.8% Guthrie County 0.2%	0.2%	2
50133	Ringgold County 97.9% Decatur County 2.1%	2.1%	2
50134	Story County 73.2% Boone County 26.8%	26.8%	2
50136	Keokuk County 94.4% Iowa County 5.6%	5.6%	2
50139	Warren County 52.8% Marion County 24.8% Lucas County 22.4%	47.2%	3
50140	Decatur County 69.2% Ringgold County 30.8%	30.8%	2
50141	Marshall County 57.1% Jasper County 42.9%	42.9%	2
50143	Mahaska County 98.7% Marion County 1.3%	1.3%	2
50146	Dallas County 88.6% Guthrie County 11.4%	11.4%	2
50147	Wayne County 52.7% Decatur County 47.3%	47.3%	2
50149	Madison County 51.1% Union County 48.9%	48.9%	2
50150	Monroe County 99.2% Marion County 0.8%	0.8%	2
50151	Lucas County 91.3% Warren County 8.7%	8.7%	2
50153	Jasper County 87.9% Mahaska County 8.8% Poweshiek County 3.3%	12.1%	3
50154	Story County 84.4% Hardin County 15.6%	15.6%	2
50155	Madison County 93.5% Adair County 6.5%	6.5%	2
50156	Boone County 77.4% Polk County 16.0% Dallas County 6.6%	22.6%	3
50158	Marshall County 98.6% Tama County 1.4%	1.4%	2
50161	Polk County 55.8% Story County 40.9% Jasper County 3.3%	44.2%	3
50162	Marshall County 96.3% Jasper County 3.7%	3.7%	2
50164	Guthrie County 52.4% Adair County 47.6%	47.6%	2
50168	Jasper County 95.8% Polk County 4.3%	4.3%	2
50169	Polk County 56.0% Jasper County 44.0%	44.0%	2
50170	Jasper County 68.7% Marion County 31.3%	31.3%	2
50171	Poweshiek County 98.3% Mahaska County 1.6%	1.6%	2
50174	Clarke County 91.1% Union County 8.9%	8.9%	2
50206	Hardin County 81.2% Marshall County 16.1% Story County 2.7%	18.8%	3
50207	Mahaska County 97.6% Poweshiek County 2.4%	2.4%	2
50210	Warren County 77.2% Clarke County 20.9% Madison County 1.9%	22.9%	3
50211	Warren County 95.9% Madison County 4.1%	4.1%	2
50217	Greene County 84.4% Boone County 15.6%	15.6%	2
50219	Marion County 63.8% Mahaska County 36.2%	36.2%	2
50220	Dallas County 63.4% Boone County 32.9% Greene County 3.7%	36.6%	3
50222	Madison County 96.6% Clarke County 3.4%	3.4%	2
50225	Marion County 84.6% Warren County 15.4%	15.4%	2
50226	Polk County 99.4% Story County 0.6%	0.6%	2
50228	Jasper County 89.5% Marion County 9.6% Polk County 0.9%	10.5%	3
50229	Warren County 51.2% Madison County 48.8%	48.8%	2
50230	Hardin County 61.0% Hamilton County 38.4% Story County 0.6%	39.0%	3
50233	Dallas County 82.1% Guthrie County 17.9%	17.9%	2
50234	Marshall County 83.1% Jasper County 16.9%	16.9%	2
50235	Greene County 85.5% Boone County 10.4% Dallas County 4.0%	14.5%	3
50237	Polk County 78.3% Jasper County 13.1% Marion County 8.6%	21.7%	3
50238	Lucas County 78.0% Wayne County 21.9%	21.9%	2
50239	Marshall County 94.0% Story County 6.0%	6.0%	2
50240	Madison County 51.4% Warren County 48.6%	48.6%	2
50243	Polk County 36.8% Story County 31.8% Boone County 31.4%	63.2%	3
50244	Polk County 59.9% Story County 38.0% Boone County 2.2%	40.1%	3
50247	Marshall County 93.5% Story County 6.5%	6.5%	2
50248	Story County 54.0% Hamilton County 35.5% Boone County 10.5%	46.0%	3
50249	Hamilton County 70.2% Webster County 19.0% Boone County 10.8%	29.8%	3
50250	Adair County 66.0% Guthrie County 34.0%	34.0%	2
50251	Jasper County 96.8% Mahaska County 3.2%	3.2%	2
50252	Marion County 62.7% Warren County 37.3%	37.3%	2
50256	Marion County 76.5% Mahaska County 23.5%	23.5%	2
50257	Madison County 75.8% Clarke County 20.5% Warren County 3.7%	24.2%	3
50258	Hardin County 71.4% Marshall County 28.6%	28.6%	2
50261	Madison County 79.5% Dallas County 20.5%	20.5%	2
50264	Clarke County 55.2% Decatur County 44.8%	44.8%	2
50265	Polk County 96.8% Warren County 3.3%	3.3%	2
50266	Dallas County 74.8% Polk County 25.2%	25.2%	2
50268	Keokuk County 81.6% Mahaska County 18.4%	18.4%	2
50271	Hamilton County 93.6% Wright County 6.4%	6.4%	2
50273	Madison County 98.8% Adair County 1.2%	1.2%	2
50275	Clarke County 94.9% Lucas County 5.1%	5.1%	2
50276	Boone County 50.9% Dallas County 49.1%	49.1%	2
50277	Guthrie County 83.0% Dallas County 17.0%	17.0%	2
50320	Polk County 77.9% Warren County 22.1%	22.1%	2
50321	Polk County 100.0% Warren County under 0.1%	under 0.1%	2
50323	Dallas County 60.5% Polk County 39.5%	39.5%	2
50325	Polk County 60.3% Dallas County 39.8%	39.8%	2
50420	Franklin County 84.8% Wright County 15.2%	15.2%	2
50424	Winnebago County 62.2% Kossuth County 37.8%	37.8%	2
50430	Hancock County 60.5% Kossuth County 36.5% Wright County 1.9% Humboldt County 1.2%	39.5%	4
50433	Cerro Gordo County 52.9% Floyd County 20.6% Franklin County 19.4% Butler County 7.1%	47.1%	4
50434	Worth County 59.6% Cerro Gordo County 40.4%	40.4%	2
50436	Winnebago County 57.9% Hancock County 42.1%	42.1%	2
50444	Worth County 94.3% Cerro Gordo County 5.7%	5.7%	2
50446	Worth County 88.5% Winnebago County 11.5%	11.5%	2
50447	Hancock County 63.8% Wright County 36.2%	36.2%	2
50449	Hancock County 90.1% Cerro Gordo County 9.9%	9.9%	2
50450	Winnebago County 68.0% Worth County 32.0%	32.0%	2
50456	Worth County 98.1% Cerro Gordo County 1.9%	1.9%	2
50457	Hancock County 30.1% Cerro Gordo County 29.7% Franklin County 27.8% Wright County 12.5%	69.9%	4
50458	Floyd County 53.3% Cerro Gordo County 35.7% Mitchell County 11.0%	46.7%	3
50459	Worth County 99.8% Winnebago County 0.2%	0.2%	2
50460	Mitchell County 77.9% Floyd County 22.1%	22.1%	2
50461	Mitchell County 99.8% Floyd County 0.2%	0.2%	2
50464	Cerro Gordo County 55.0% Worth County 42.4% Mitchell County 2.7%	45.0%	3
50466	Howard County 60.3% Mitchell County 39.7%	39.7%	2
50468	Floyd County 75.3% Cerro Gordo County 24.7%	24.7%	2
50470	Wright County 96.5% Franklin County 3.5%	3.5%	2
50471	Floyd County 94.0% Mitchell County 6.0%	6.0%	2
50472	Mitchell County 84.8% Worth County 15.2%	15.2%	2
50475	Franklin County 76.8% Cerro Gordo County 23.2%	23.2%	2
50479	Cerro Gordo County 72.5% Franklin County 27.5%	27.5%	2
50480	Kossuth County 96.6% Hancock County 2.2% Winnebago County 1.1%	3.4%	3
50482	Cerro Gordo County 78.0% Hancock County 22.0%	22.0%	2
50483	Kossuth County 70.5% Hancock County 29.4%	29.4%	2
50484	Hancock County 64.5% Winnebago County 33.2% Kossuth County 2.3%	35.5%	3
50510	Buena Vista County 84.4% Pocahontas County 15.6%	15.6%	2
50514	Emmet County 64.7% Kossuth County 35.3%	35.3%	2
50515	Palo Alto County 76.7% Clay County 23.3%	23.3%	2
50516	Webster County 76.4% Humboldt County 23.6%	23.6%	2
50519	Humboldt County 55.0% Kossuth County 45.0%	45.0%	2
50520	Humboldt County 93.4% Pocahontas County 6.6%	6.6%	2
50524	Webster County 95.7% Pocahontas County 4.3%	4.3%	2
50530	Webster County 96.0% Boone County 4.0%	4.0%	2
50532	Webster County 90.2% Hamilton County 9.8%	9.8%	2
50533	Wright County 79.5% Humboldt County 11.1% Webster County 9.4%	20.5%	3
50538	Calhoun County 93.0% Webster County 7.0%	7.0%	2
50539	Kossuth County 77.7% Palo Alto County 22.3%	22.3%	2
50540	Pocahontas County 72.4% Calhoun County 25.0% Sac County 2.6%	27.6%	3
50541	Pocahontas County 52.7% Humboldt County 47.3%	47.3%	2
50542	Wright County 68.5% Humboldt County 31.5%	31.5%	2
50546	Pocahontas County 95.3% Palo Alto County 4.7%	4.7%	2
50548	Humboldt County 92.3% Webster County 7.7%	7.7%	2
50554	Pocahontas County 84.8% Palo Alto County 11.9% Buena Vista County 3.4%	15.2%	3
50558	Humboldt County 82.9% Kossuth County 17.1%	17.1%	2
50560	Kossuth County 85.4% Humboldt County 14.6%	14.6%	2
50561	Calhoun County 57.7% Sac County 42.3%	42.3%	2
50562	Palo Alto County 92.9% Pocahontas County 7.1%	7.1%	2
50563	Calhoun County 68.8% Pocahontas County 26.4% Webster County 4.8%	31.2%	3
50565	Buena Vista County 95.4% Clay County 4.6%	4.6%	2
50566	Webster County 96.7% Calhoun County 3.3%	3.3%	2
50568	Buena Vista County 88.3% Sac County 11.7%	11.7%	2
50570	Humboldt County 64.2% Kossuth County 35.8%	35.8%	2
50575	Calhoun County 53.1% Pocahontas County 46.9%	46.9%	2
50577	Humboldt County 57.2% Wright County 42.8%	42.8%	2
50578	Emmet County 89.5% Palo Alto County 10.4%	10.4%	2
50581	Pocahontas County 91.9% Palo Alto County 8.1%	8.1%	2
50583	Sac County 97.4% Calhoun County 2.6%	2.6%	2
50585	Buena Vista County 51.7% Clay County 48.3%	48.3%	2
50586	Calhoun County 93.1% Webster County 6.9%	6.9%	2
50588	Buena Vista County 99.3% Sac County 0.7%	0.7%	2
50591	Humboldt County 88.1% Webster County 11.9%	11.9%	2
50595	Hamilton County 97.9% Wright County 1.4% Webster County 0.7%	2.1%	3
50597	Palo Alto County 55.4% Kossuth County 42.3% Humboldt County 1.4% Pocahontas County 0.9%	44.6%	4
50598	Kossuth County 70.1% Palo Alto County 29.9%	29.9%	2
50599	Wright County 83.6% Hamilton County 16.4%	16.4%	2
50601	Franklin County 36.5% Hardin County 29.9% Butler County 17.7% Grundy County 16.0%	63.5%	4
50603	Chickasaw County 83.3% Howard County 16.7%	16.7%	2
50604	Butler County 79.5% Grundy County 20.5%	20.5%	2
50605	Franklin County 61.1% Butler County 38.9%	38.9%	2
50606	Fayette County 95.7% Clayton County 4.3%	4.3%	2
50607	Buchanan County 70.4% Fayette County 29.6%	29.6%	2
50609	Grundy County 65.9% Marshall County 30.7% Tama County 3.4%	34.1%	3
50612	Tama County 72.5% Black Hawk County 27.4%	27.4%	2
50613	Black Hawk County 80.7% Grundy County 15.4% Butler County 3.8%	19.3%	3
50616	Floyd County 93.7% Chickasaw County 6.3%	6.3%	2
50621	Grundy County 83.8% Marshall County 16.2%	16.2%	2
50625	Butler County 82.8% Franklin County 17.2%	17.2%	2
50626	Black Hawk County 99.6% Buchanan County 0.4%	0.4%	2
50627	Hardin County 82.7% Grundy County 17.3%	17.3%	2
50628	Howard County 93.0% Mitchell County 7.0%	7.0%	2
50629	Buchanan County 32.4% Bremer County 29.4% Fayette County 22.1% Black Hawk County 16.2%	67.6%	4
50630	Chickasaw County 89.8% Bremer County 10.2%	10.2%	2
50632	Tama County 98.7% Marshall County 1.3%	1.3%	2
50635	Tama County 96.0% Marshall County 4.0%	4.0%	2
50636	Butler County 62.2% Floyd County 37.8%	37.8%	2
50643	Black Hawk County 90.6% Grundy County 9.4%	9.4%	2
50645	Chickasaw County 90.2% Bremer County 6.8% Floyd County 2.9%	9.8%	3
50647	Bremer County 62.0% Black Hawk County 38.0%	38.0%	2
50648	Black Hawk County 58.4% Buchanan County 41.6%	41.6%	2
50650	Buchanan County 69.1% Fayette County 30.9%	30.9%	2
50651	Black Hawk County 71.3% Benton County 26.0% Tama County 2.8%	28.7%	3
50654	Buchanan County 52.0% Delaware County 48.0%	48.0%	2
50658	Chickasaw County 55.2% Floyd County 34.0% Butler County 6.6% Bremer County 4.2%	44.8%	4
50660	Butler County 78.9% Grundy County 21.1%	21.1%	2
50662	Fayette County 93.7% Buchanan County 6.3%	6.3%	2
50665	Butler County 64.4% Grundy County 35.6%	35.6%	2
50666	Bremer County 76.0% Butler County 24.0%	24.0%	2
50669	Grundy County 69.1% Tama County 29.9% Black Hawk County 1.0%	30.9%	3
50670	Butler County 97.3% Bremer County 1.8% Black Hawk County 0.9%	2.7%	3
50671	Fayette County 60.8% Buchanan County 39.2%	39.2%	2
50672	Hardin County 90.7% Grundy County 9.3%	9.3%	2
50674	Bremer County 61.5% Fayette County 32.5% Chickasaw County 6.0%	38.5%	3
50675	Tama County 97.8% Black Hawk County 2.2%	2.2%	2
50677	Bremer County 96.9% Butler County 3.1%	3.1%	2
50680	Grundy County 99.2% Hardin County 0.8%	0.8%	2
50801	Union County 68.6% Adams County 20.6% Adair County 10.8%	31.4%	3
50836	Taylor County 59.7% Ringgold County 40.3%	40.3%	2
50837	Adair County 70.0% Cass County 16.5% Adams County 13.4%	30.0%	3
50840	Taylor County 60.6% Ringgold County 39.4%	39.4%	2
50841	Adams County 89.0% Taylor County 11.1%	11.1%	2
50843	Cass County 92.3% Adams County 7.7%	7.7%	2
50845	Ringgold County 91.6% Union County 8.4%	8.4%	2
50851	Taylor County 44.2% Adams County 34.1% Union County 17.3% Ringgold County 4.4%	55.8%	4
50853	Cass County 98.1% Adams County 1.9%	1.9%	2
50857	Adams County 72.8% Taylor County 25.9% Montgomery County 1.4%	27.2%	3
50859	Adams County 95.4% Adair County 4.6%	4.6%	2
50861	Union County 68.6% Ringgold County 31.4%	31.4%	2
50864	Montgomery County 65.5% Page County 19.9% Taylor County 8.9% Adams County 3.9% Cass County 1.7%	34.5%	5
51001	Plymouth County 60.2% Union County, SD 39.8%	39.8%	2
51002	Buena Vista County 98.6% Cherokee County 1.4%	1.4%	2
51005	Cherokee County 86.1% Buena Vista County 13.9%	13.9%	2
51006	Ida County 85.8% Woodbury County 12.3% Crawford County 1.9%	14.2%	3
51016	Woodbury County 90.5% Ida County 9.5%	9.5%	2
51018	Ida County 56.3% Woodbury County 43.7%	43.7%	2
51019	Woodbury County 79.2% Ida County 11.8% Crawford County 8.2% Monona County 0.8%	20.8%	4
51020	Ida County 71.5% Sac County 12.9% Cherokee County 12.0% Buena Vista County 3.6%	28.5%	4
51022	O'Brien County 57.9% Sioux County 39.5% Plymouth County 2.5%	42.1%	3
51023	Sioux County 70.2% Union County, SD 29.8%	29.8%	2
51025	Ida County 87.3% Cherokee County 12.7%	12.7%	2
51026	Woodbury County 64.7% Monona County 35.3%	35.3%	2
51027	Sioux County 83.9% Plymouth County 16.1%	16.1%	2
51028	Plymouth County 80.0% Woodbury County 20.0%	20.0%	2
51029	Cherokee County 85.2% O'Brien County 14.8%	14.8%	2
51031	Plymouth County 98.9% Sioux County 1.1%	1.1%	2
51033	Clay County 50.1% Buena Vista County 49.9%	49.9%	2
51034	Monona County 80.5% Woodbury County 15.7% Crawford County 3.8%	19.5%	3
51035	Cherokee County 99.0% Plymouth County 1.0%	1.0%	2
51046	O'Brien County 94.6% Cherokee County 5.4%	5.4%	2
51047	Clay County 55.0% Buena Vista County 26.6% Cherokee County 13.3% O'Brien County 5.1%	45.0%	4
51048	Woodbury County 48.7% Cherokee County 40.0% Plymouth County 11.3%	51.3%	3
51050	Plymouth County 98.6% Sioux County 1.4%	1.4%	2
51053	Sac County 89.3% Ida County 10.8%	10.8%	2
51055	Woodbury County 51.4% Monona County 48.6%	48.6%	2
51056	Woodbury County 85.3% Monona County 14.7%	14.7%	2
51058	O'Brien County 92.6% Cherokee County 6.2% Clay County 1.2%	7.4%	3
51060	Monona County 76.7% Crawford County 23.4%	23.4%	2
51061	Cherokee County 79.4% Ida County 20.6%	20.6%	2
51108	Plymouth County 53.3% Woodbury County 46.8%	46.8%	2
51109	Plymouth County 89.7% Woodbury County 10.3%	10.3%	2
51201	Sioux County 49.2% O'Brien County 48.6% Lyon County 2.2%	50.8%	3
51232	Osceola County 72.7% Lyon County 25.7% O'Brien County 1.6%	27.3%	3
51235	Lyon County 96.9% Sioux County 3.1%	3.1%	2
51238	Sioux County 67.7% O'Brien County 32.3%	32.3%	2
51239	Sioux County 92.7% Lyon County 7.3%	7.3%	2
51240	Lyon County 85.5% Sioux County 14.5%	14.5%	2
51243	Lyon County 86.0% Osceola County 14.0%	14.0%	2
51247	Sioux County 95.5% Lyon County 4.5%	4.5%	2
51248	O'Brien County 89.8% Osceola County 10.2%	10.2%	2
51334	Emmet County 89.1% Dickinson County 10.9%	10.9%	2
51338	Clay County 79.1% Dickinson County 20.9%	20.9%	2
51342	Palo Alto County 66.0% Emmet County 34.0%	34.0%	2
51345	Osceola County 97.3% Dickinson County 2.8%	2.8%	2
51346	O'Brien County 71.4% Osceola County 20.4% Clay County 8.2%	28.6%	3
51350	Osceola County 93.4% O'Brien County 6.6%	6.6%	2
51358	Palo Alto County 64.2% Clay County 35.8%	35.8%	2
51360	Dickinson County 97.0% Jackson County, MN 3.0%	3.0%	2
51364	Dickinson County 75.6% Clay County 12.8% Emmet County 11.5%	24.4%	3
51366	Clay County 97.3% Buena Vista County 2.7%	2.7%	2
51431	Ida County 89.0% Sac County 11.0%	11.0%	2
51433	Sac County 58.3% Calhoun County 41.8%	41.8%	2
51436	Carroll County 68.5% Crawford County 18.4% Sac County 13.1%	31.5%	3
51448	Crawford County 61.6% Sac County 19.9% Ida County 18.4%	38.4%	3
51449	Calhoun County 87.8% Carroll County 12.2%	12.2%	2
51453	Calhoun County 90.6% Carroll County 8.2% Greene County 1.2%	9.4%	3
51454	Crawford County 57.5% Shelby County 42.5%	42.5%	2
51455	Carroll County 55.7% Crawford County 23.5% Audubon County 18.3% Shelby County 2.5%	44.3%	4
51461	Crawford County 92.7% Ida County 7.3%	7.3%	2
51462	Greene County 97.4% Carroll County 2.6%	2.6%	2
51466	Sac County 98.6% Crawford County 1.4%	1.4%	2
51467	Crawford County 70.0% Carroll County 30.0%	30.0%	2
51503	Pottawattamie County 84.6% Mills County 15.4%	15.4%	2
51521	Pottawattamie County 69.0% Shelby County 31.0%	31.0%	2
51523	Monona County 92.0% Harrison County 8.0%	8.0%	2
51527	Shelby County 83.3% Crawford County 16.7%	16.7%	2
51529	Harrison County 38.3% Crawford County 28.1% Monona County 18.2% Shelby County 15.4%	61.7%	4
51531	Shelby County 78.5% Audubon County 21.4%	21.4%	2
51532	Montgomery County 86.2% Pottawattamie County 10.9% Cass County 2.9%	13.8%	3
51533	Montgomery County 54.8% Mills County 45.2%	45.2%	2
51535	Cass County 56.5% Pottawattamie County 43.5%	43.5%	2
51541	Mills County 70.9% Montgomery County 15.9% Pottawattamie County 13.2%	29.1%	3
51543	Audubon County 69.9% Shelby County 30.1%	30.1%	2
51544	Cass County 74.0% Pottawattamie County 26.0%	26.0%	2
51545	Harrison County 72.2% Monona County 27.8%	27.8%	2
51552	Cass County 63.1% Shelby County 36.9%	36.9%	2
51555	Harrison County 81.6% Pottawattamie County 18.4%	18.4%	2
51557	Harrison County 89.7% Burt County, NE 10.3%	10.3%	2
51558	Monona County 90.8% Harrison County 9.2%	9.2%	2
51559	Pottawattamie County 84.0% Harrison County 16.0%	16.0%	2
51563	Harrison County 99.7% Shelby County 0.3%	0.3%	2
51565	Shelby County 74.0% Harrison County 26.0%	26.0%	2
51566	Montgomery County 91.4% Page County 6.6% Pottawattamie County 2.0%	8.6%	3
51570	Shelby County 53.5% Pottawattamie County 33.0% Harrison County 13.6%	46.5%	3
51571	Mills County 66.1% Pottawattamie County 33.9%	33.9%	2
51577	Pottawattamie County 66.5% Shelby County 31.2% Cass County 2.3%	33.5%	3
51601	Page County 62.7% Fremont County 37.3%	37.3%	2
51632	Page County 98.5% Taylor County 1.5%	1.5%	2
51638	Page County 98.0% Montgomery County 2.0%	2.0%	2
51640	Fremont County 81.9% Atchison County, MO 18.1%	18.1%	2
51645	Fremont County 57.5% Mills County 30.1% Montgomery County 7.0% Page County 5.5%	42.5%	4
51647	Page County 75.2% Fremont County 24.8%	24.8%	2
51653	Fremont County 74.6% Mills County 25.4%	25.4%	2
52031	Jackson County 94.7% Dubuque County 5.3%	5.3%	2
52032	Dubuque County 47.0% Jackson County 45.6% Jones County 7.4%	53.0%	3
52033	Jones County 58.0% Dubuque County 42.0%	42.0%	2
52035	Clayton County 62.3% Delaware County 37.7%	37.7%	2
52037	Clinton County 97.8% Jackson County 2.2%	2.2%	2
52040	Delaware County 53.6% Dubuque County 46.4%	46.4%	2
52042	Clayton County 81.3% Delaware County 18.7%	18.7%	2
52050	Delaware County 88.3% Clayton County 11.7%	11.7%	2
52052	Clayton County 89.5% Dubuque County 10.5%	10.5%	2
52053	Dubuque County 78.3% Clayton County 21.7%	21.7%	2
52054	Jackson County 93.0% Dubuque County 7.0%	7.0%	2
52060	Jackson County 88.1% Clinton County 11.9%	11.9%	2
52064	Jackson County 85.9% Clinton County 14.1%	14.1%	2
52065	Dubuque County 74.8% Delaware County 25.2%	25.2%	2
52069	Jackson County 77.6% Clinton County 22.4%	22.4%	2
52070	Jackson County 84.5% Clinton County 15.5%	15.5%	2
52073	Dubuque County 92.4% Clayton County 7.6%	7.6%	2
52076	Clayton County 82.8% Delaware County 16.5% Fayette County 0.7%	17.2%	3
52078	Dubuque County 64.2% Delaware County 35.8%	35.8%	2
52079	Jackson County 54.5% Dubuque County 45.5%	45.5%	2
52101	Winneshiek County 97.1% Allamakee County 2.9%	2.9%	2
52132	Winneshiek County 98.3% Howard County 1.7%	1.7%	2
52133	Winneshiek County 70.2% Fayette County 29.8%	29.8%	2
52135	Fayette County 92.5% Clayton County 7.5%	7.5%	2
52136	Howard County 66.9% Winneshiek County 33.1%	33.1%	2
52140	Allamakee County 91.1% Winneshiek County 8.9%	8.9%	2
52141	Fayette County 58.5% Clayton County 41.5%	41.5%	2
52144	Winneshiek County 94.3% Fayette County 5.7%	5.7%	2
52154	Chickasaw County 98.6% Howard County 1.4%	1.4%	2
52156	Clayton County 72.6% Allamakee County 27.4%	27.4%	2
52159	Allamakee County 50.8% Clayton County 49.3%	49.3%	2
52161	Winneshiek County 86.2% Fayette County 13.8%	13.8%	2
52162	Allamakee County 59.9% Clayton County 27.4% Winneshiek County 9.6% Fayette County 3.1%	40.1%	4
52169	Fayette County 94.0% Clayton County 6.0%	6.0%	2
52171	Fayette County 50.4% Chickasaw County 31.1% Winneshiek County 18.4%	49.6%	3
52172	Allamakee County 95.5% Winneshiek County 4.5%	4.5%	2
52203	Iowa County 78.7% Johnson County 21.3% Linn County under 0.1%	21.3%	3
52205	Jones County 85.2% Linn County 14.8%	14.8%	2
52207	Jackson County 87.2% Clinton County 12.8%	12.8%	2
52208	Benton County 55.8% Iowa County 27.4% Tama County 13.5% Poweshiek County 3.4%	44.2%	4
52209	Benton County 96.3% Iowa County 3.8%	3.8%	2
52210	Buchanan County 98.6% Benton County 1.4%	1.4%	2
52213	Linn County 76.4% Benton County 23.6%	23.6%	2
52215	Tama County 81.0% Poweshiek County 19.0%	19.0%	2
52216	Cedar County 85.9% Jones County 14.1%	14.1%	2
52218	Linn County 55.5% Buchanan County 24.3% Delaware County 20.2%	44.5%	3
52221	Poweshiek County 84.7% Iowa County 15.3%	15.3%	2
52222	Poweshiek County 70.8% Iowa County 29.2%	29.2%	2
52224	Benton County 52.2% Tama County 47.8%	47.8%	2
52225	Tama County 72.4% Benton County 27.6%	27.6%	2
52227	Linn County 93.4% Johnson County 6.6%	6.6%	2
52228	Linn County 75.7% Benton County 13.1% Johnson County 11.2%	24.3%	3
52237	Delaware County 95.6% Jones County 2.9% Dubuque County 1.5%	4.4%	3
52247	Johnson County 55.0% Washington County 45.0%	45.0%	2
52248	Washington County 51.6% Keokuk County 48.4%	48.4%	2
52253	Cedar County 49.9% Linn County 23.6% Jones County 17.7% Johnson County 8.8%	50.1%	4
52301	Iowa County 96.4% Benton County 3.6%	3.6%	2
52305	Jones County 78.1% Linn County 21.9%	21.9%	2
52306	Cedar County 79.4% Jones County 20.6%	20.6%	2
52309	Jackson County 72.1% Jones County 27.9%	27.9%	2
52310	Jones County 95.3% Linn County 4.2% Delaware County 0.5%	4.7%	3
52316	Iowa County 87.2% Keokuk County 12.8%	12.8%	2
52318	Benton County 81.7% Iowa County 18.4%	18.4%	2
52320	Jones County 87.0% Cedar County 13.0%	13.0%	2
52322	Johnson County 99.2% Iowa County 0.8%	0.8%	2
52323	Jones County 78.2% Clinton County 13.2% Cedar County 8.6%	21.8%	3
52324	Linn County 81.6% Benton County 18.4%	18.4%	2
52325	Iowa County 86.2% Johnson County 13.8%	13.8%	2
52327	Washington County 72.7% Johnson County 27.1% Louisa County 0.1%	27.3%	3
52332	Benton County 92.2% Linn County 7.8%	7.8%	2
52333	Johnson County 95.8% Cedar County 4.2%	4.2%	2
52338	Johnson County 93.9% Linn County 6.1%	6.1%	2
52339	Tama County 97.3% Poweshiek County 2.7%	2.7%	2
52347	Iowa County 67.0% Poweshiek County 33.0%	33.0%	2
52351	Benton County 67.7% Linn County 32.3%	32.3%	2
52352	Linn County 47.2% Buchanan County 36.3% Benton County 16.5%	52.8%	3
52355	Keokuk County 91.9% Iowa County 8.1%	8.1%	2
52356	Washington County 73.7% Iowa County 16.8% Johnson County 8.2% Keokuk County 1.3%	26.3%	4
52358	Cedar County 82.5% Johnson County 17.5%	17.5%	2
52404	Linn County 95.0% Johnson County 5.0%	5.0%	2
52501	Wapello County 99.3% Keokuk County 0.4% Mahaska County 0.2%	0.7%	3
52531	Monroe County 99.0% Wapello County 0.9%	0.9%	2
52533	Jefferson County 68.9% Wapello County 31.1%	31.1%	2
52535	Van Buren County 82.7% Jefferson County 17.3%	17.3%	2
52536	Wapello County 67.6% Monroe County 32.4%	32.4%	2
52537	Davis County 95.5% Wapello County 4.5%	4.5%	2
52540	Jefferson County 53.5% Washington County 46.5%	46.5%	2
52542	Van Buren County 80.5% Scotland County, MO 19.5%	19.5%	2
52550	Keokuk County 97.7% Mahaska County 2.4%	2.4%	2
52551	Van Buren County 91.9% Davis County 8.1%	8.1%	2
52552	Davis County 95.9% Wapello County 4.1%	4.1%	2
52553	Wapello County 36.7% Mahaska County 34.0% Monroe County 29.3%	63.3%	3
52554	Wapello County 76.1% Davis County 10.5% Jefferson County 9.3% Van Buren County 4.1%	23.9%	4
52561	Mahaska County 83.7% Keokuk County 16.3%	16.3%	2
52563	Keokuk County 58.2% Wapello County 38.3% Jefferson County 3.5%	41.8%	3
52567	Jefferson County 89.3% Van Buren County 10.7%	10.7%	2
52569	Monroe County 82.9% Wayne County 6.1% Lucas County 6.0% Appanoose County 5.0%	17.1%	4
52570	Van Buren County 73.7% Davis County 26.3%	26.3%	2
52571	Appanoose County 70.3% Monroe County 29.7%	29.7%	2
52572	Appanoose County 84.2% Davis County 15.8%	15.8%	2
52573	Van Buren County 65.3% Clark County, MO 23.8% Scotland County, MO 10.9%	34.7%	3
52576	Keokuk County 98.9% Jefferson County 1.1%	1.1%	2
52580	Jefferson County 97.6% Keokuk County 2.4%	2.4%	2
52581	Appanoose County 96.1% Wayne County 3.9%	3.9%	2
52585	Keokuk County 60.2% Jefferson County 29.2% Washington County 10.6%	39.8%	3
52586	Mahaska County 96.9% Keokuk County 3.1%	3.1%	2
52588	Van Buren County 66.2% Davis County 31.8% Jefferson County 2.0%	33.8%	3
52590	Wayne County 78.9% Appanoose County 21.1%	21.1%	2
52594	Appanoose County 61.8% Davis County 38.2%	38.2%	2
52621	Washington County 84.6% Louisa County 15.4%	15.4%	2
52623	Des Moines County 77.5% Henry County 22.5%	22.5%	2
52626	Lee County 54.5% Van Buren County 23.9% Clark County, MO 21.6%	45.5%	3
52630	Lee County 38.8% Van Buren County 33.3% Henry County 27.9%	61.2%	3
52635	Jefferson County 93.5% Henry County 6.5%	6.5%	2
52640	Louisa County 66.6% Des Moines County 33.4%	33.4%	2
52641	Henry County 96.1% Washington County 2.2% Jefferson County 1.7%	3.9%	3
52644	Henry County 85.1% Des Moines County 14.9%	14.9%	2
52645	Henry County 70.0% Des Moines County 30.0%	30.0%	2
52646	Des Moines County 52.6% Louisa County 47.4%	47.4%	2
52649	Henry County 74.6% Lee County 25.4%	25.4%	2
52651	Van Buren County 89.5% Jefferson County 10.5%	10.5%	2
52654	Henry County 67.2% Washington County 30.4% Jefferson County 2.3%	32.8%	3
52656	Lee County 98.8% Henry County 1.2%	1.2%	2
52658	Lee County 98.2% Des Moines County 1.8%	1.8%	2
52659	Henry County 70.6% Louisa County 29.4%	29.4%	2
52720	Muscatine County 62.5% Cedar County 37.5%	37.5%	2
52726	Scott County 54.8% Muscatine County 45.2%	45.2%	2
52729	Clinton County 99.0% Scott County 1.0%	1.0%	2
52731	Clinton County 98.2% Jackson County 1.8%	1.8%	2
52738	Louisa County 97.3% Washington County 2.7%	2.7%	2
52739	Louisa County 56.0% Muscatine County 44.0%	44.0%	2
52747	Muscatine County 45.4% Cedar County 36.1% Scott County 18.4%	54.6%	3
52754	Muscatine County 53.5% Louisa County 46.5%	46.5%	2
52755	Johnson County 91.6% Louisa County 8.4%	8.4%	2
52760	Muscatine County 58.9% Cedar County 41.1%	41.1%	2
52761	Muscatine County 90.6% Louisa County 9.4%	9.4%	2
52765	Scott County 77.0% Cedar County 23.0%	23.0%	2
52766	Muscatine County 94.4% Johnson County 5.6%	5.6%	2
52769	Scott County 50.9% Muscatine County 49.1%	49.1%	2
52773	Scott County 96.5% Muscatine County 3.5%	3.5%	2
52776	Muscatine County 62.4% Cedar County 34.3% Johnson County 3.3%	37.6%	3
52777	Clinton County 92.5% Cedar County 7.5%	7.5%	2
52778	Cedar County 60.4% Muscatine County 39.6%	39.6%	2
56027	Faribault County, MN 77.1% Kossuth County 13.4% Martin County, MN 9.5%	22.9%	3
57034	Lincoln County, SD 83.6% Union County, SD 8.7% Sioux County 7.7%	16.4%	3

What to do with this

If a ZIP code in your list is split, the ZIP alone cannot tell you which county an address is in. For most work that is fine. It matters when the county decides something: a sales tax rate, a licence, a franchise agreement written by county, or a service area somebody promised by county name.

The ZIP list audit checks your own list against the same Census data in your browser, and the ZIP spreadsheet comparison covers when a ZIP list is enough and when it is not.

What these numbers are, and are not

A ZCTA is not quite a ZIP code. ZIP Code Tabulation Areas are the Census Bureau's approximations of ZIP code areas, built by grouping census blocks by the ZIP codes of the addresses in them. USPS ZIP codes are delivery routes, not areas, and the two do not always match.
Some ZIP codes have no ZCTA at all. PO box ZIPs, ZIPs for a single building or a single large organisation, and military ZIPs usually have no area of their own, so they cannot be split across counties here and will not match any area in a map.
Land share is not population share. A ZCTA with 20% of its land in a second county might have almost none of its people there, or most of them. The shares here measure area, which is what the Census file publishes.
Tiny overlaps are included. A ZCTA counts as overlapping a county if the Census file lists any part of it there, including slivers along a road or river. That is why the share with at least 5% of land in a second county is shown alongside.

Source: U.S. Census Bureau, 2020 ZCTA to County relationship file, public domain. Counts use 2020 ZCTAs and 2020 county boundaries. ZIP codes added by USPS since then are not in it, and Connecticut's counties have since been replaced by planning regions in Census data.

Route by the boundary, not the ZIP

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