ZIP codes and county lines in Montana

125 of the 373 ZIP code areas in Montana, or 33.5%, 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: 373
In more than one county: 125
At least 5% in a second county: 96
Cross a state line: 8

How Montana compares

Montana ranks 25 of 52 (the 50 states, DC and Puerto Rico) by the share of its ZIP code areas that overlap more than one county. 55 of its counties have at least one split ZIP code area along an edge. 8 of its ZIP code areas also reach into Idaho, North Dakota, South Dakota and Wyoming, so a ZIP list that is meant to stop at the state line does not.

Counties with the most split ZIP code areas

Cascade County: 10 ZIP codes shared with another county
Roosevelt County: 9 ZIP codes shared with another county
Yellowstone County: 9 ZIP codes shared with another county
Big Horn County: 8 ZIP codes shared with another county
Chouteau County: 8 ZIP codes shared with another county

Every split ZIP code area in Montana

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
57717	Butte County, SD 65.5% Crook County, WY 15.2% Carter County 10.2% Harding County, SD 8.6% Lawrence County, SD 0.6%	34.5%	5
57724	Harding County, SD 62.6% Carter County 37.4%	37.4%	2
58621	Golden Valley County, ND 90.7% Wibaux County 4.4% McKenzie County, ND 2.8% Billings County, ND 2.1%	9.3%	4
59001	Stillwater County 94.3% Carbon County 5.7%	5.7%	2
59003	Powder River County 61.5% Rosebud County 38.5%	38.5%	2
59010	Treasure County 54.8% Big Horn County 45.2%	45.2%	2
59015	Yellowstone County 51.7% Stillwater County 28.9% Musselshell County 19.4%	48.3%	3
59019	Stillwater County 97.9% Carbon County 2.1%	2.1%	2
59024	Yellowstone County 92.0% Big Horn County 8.0%	8.0%	2
59032	Fergus County 76.7% Petroleum County 23.4%	23.4%	2
59037	Yellowstone County 92.7% Big Horn County 7.3%	7.3%	2
59038	Treasure County 87.1% Big Horn County 12.9%	12.9%	2
59041	Carbon County 97.4% Yellowstone County 2.6%	2.6%	2
59043	Rosebud County 70.0% Big Horn County 30.0%	30.0%	2
59044	Yellowstone County 91.2% Carbon County 8.8%	8.8%	2
59046	Golden Valley County 91.7% Musselshell County 8.3%	8.3%	2
59052	Sweet Grass County 58.8% Park County 41.2%	41.2%	2
59053	Meagher County 96.8% Wheatland County 3.2%	3.2%	2
59054	Rosebud County 57.6% Musselshell County 42.4%	42.4%	2
59057	Stillwater County 68.5% Yellowstone County 31.5%	31.5%	2
59058	Garfield County 74.4% Petroleum County 25.6%	25.6%	2
59062	Powder River County 69.1% Rosebud County 30.9%	30.9%	2
59063	Stillwater County 99.6% Yellowstone County 0.4%	0.4%	2
59064	Big Horn County 71.8% Yellowstone County 28.2%	28.2%	2
59069	Stillwater County 50.6% Sweet Grass County 49.4%	49.4%	2
59072	Musselshell County 93.1% Petroleum County 6.9%	6.9%	2
59074	Golden Valley County 91.4% Stillwater County 6.8% Wheatland County 1.8%	8.6%	3
59078	Wheatland County 69.4% Golden Valley County 22.4% Sweet Grass County 8.2%	30.6%	3
59082	Park County 65.8% Sweet Grass County 34.2%	34.2%	2
59086	Park County 66.2% Gallatin County 31.5% Meagher County 2.3%	33.8%	3
59101	Yellowstone County 97.7% Big Horn County 2.3%	2.3%	2
59201	Roosevelt County 54.3% McCone County 37.8% Valley County 8.0%	45.7%	3
59213	Roosevelt County 56.5% Richland County 43.5%	43.5%	2
59214	McCone County 83.6% Prairie County 11.3% Garfield County 5.2%	16.4%	3
59215	McCone County 90.9% Dawson County 9.1%	9.1%	2
59218	Roosevelt County 50.4% Richland County 49.6%	49.6%	2
59221	Richland County 84.7% McKenzie County, ND 15.3%	15.3%	2
59222	Daniels County 98.4% Roosevelt County 1.6%	1.6%	2
59223	McCone County 91.1% Garfield County 8.4% Valley County 0.5%	8.9%	3
59226	Roosevelt County 87.1% Sheridan County 12.9%	12.9%	2
59241	Valley County 100.0% Phillips County under 0.1%	under 0.1%	2
59242	Sheridan County 57.9% Roosevelt County 42.1%	42.1%	2
59253	Daniels County 98.0% Valley County 2.0%	2.0%	2
59255	Roosevelt County 77.5% Richland County 19.4% McCone County 3.0%	22.5%	3
59258	Sheridan County 64.4% Roosevelt County 35.6%	35.6%	2
59259	Dawson County 54.5% Richland County 45.5%	45.5%	2
59260	Valley County 60.9% Daniels County 39.1%	39.1%	2
59261	Phillips County 78.7% Valley County 21.3%	21.3%	2
59262	Richland County 57.3% Dawson County 42.7%	42.7%	2
59263	Daniels County 98.0% Roosevelt County 2.0%	2.0%	2
59270	Richland County 60.4% McKenzie County, ND 39.6%	39.6%	2
59275	Sheridan County 76.3% Divide County, ND 23.8%	23.8%	2
59301	Custer County 81.3% Rosebud County 10.0% Garfield County 5.1% Powder River County 2.3% Prairie County 1.4%	18.7%	5
59313	Fallon County 93.6% Carter County 6.4%	6.4%	2
59316	Powder River County 70.3% Carter County 29.6%	29.6%	2
59326	Prairie County 88.2% Dawson County 11.8%	11.8%	2
59330	Dawson County 96.9% Prairie County 3.1%	3.1%	2
59336	Custer County 65.5% Fallon County 28.2% Carter County 5.7% Prairie County 0.7%	34.5%	4
59339	Dawson County 98.9% Prairie County 1.1%	1.1%	2
59344	Fallon County 93.9% Carter County 6.1%	6.1%	2
59345	Custer County 68.0% Powder River County 32.0%	32.0%	2
59347	Rosebud County 92.4% Custer County 7.6%	7.6%	2
59349	Prairie County 98.7% Custer County 1.3%	1.3%	2
59351	Powder River County 60.5% Custer County 39.5%	39.5%	2
59353	Wibaux County 83.9% Dawson County 13.9% Fallon County 2.2%	16.1%	3
59404	Cascade County 71.5% Chouteau County 28.5%	28.5%	2
59405	Cascade County 98.8% Chouteau County 1.1%	1.1%	2
59410	Lewis and Clark County 97.7% Teton County 2.4%	2.4%	2
59412	Cascade County 96.9% Judith Basin County 3.1%	3.1%	2
59416	Pondera County 56.3% Chouteau County 41.1% Teton County 1.5% Liberty County 1.1%	43.8%	4
59418	Judith Basin County 76.9% Fergus County 23.1%	23.1%	2
59421	Cascade County 95.5% Lewis and Clark County 4.5%	4.5%	2
59424	Fergus County 66.7% Judith Basin County 33.3%	33.3%	2
59425	Pondera County 91.1% Teton County 8.9%	8.9%	2
59427	Glacier County 97.3% Toole County 2.8%	2.8%	2
59430	Fergus County 94.6% Judith Basin County 5.4%	5.4%	2
59432	Pondera County 72.9% Teton County 27.1%	27.1%	2
59436	Teton County 99.6% Cascade County 0.4%	0.4%	2
59440	Chouteau County 68.0% Cascade County 32.0%	32.0%	2
59443	Cascade County 93.5% Teton County 6.5%	6.5%	2
59444	Toole County 80.3% Liberty County 19.6%	19.6%	2
59447	Judith Basin County 97.0% Chouteau County 3.0%	3.0%	2
59448	Pondera County 99.1% Glacier County 0.9%	0.9%	2
59453	Wheatland County 76.6% Fergus County 18.5% Judith Basin County 4.9%	23.4%	3
59456	Liberty County 51.5% Toole County 38.6% Pondera County 9.8%	48.5%	3
59463	Cascade County 94.0% Judith Basin County 6.0%	6.0%	2
59464	Fergus County 94.6% Judith Basin County 5.4%	5.4%	2
59468	Teton County 71.2% Cascade County 28.8%	28.8%	2
59487	Cascade County 92.3% Teton County 7.7%	7.7%	2
59501	Hill County 95.8% Blaine County 4.3%	4.3%	2
59520	Chouteau County 97.1% Blaine County 2.3% Hill County 0.5%	2.9%	3
59521	Hill County 81.6% Chouteau County 18.4%	18.4%	2
59523	Blaine County 98.9% Hill County 1.1%	1.1%	2
59524	Phillips County 88.0% Blaine County 12.0%	12.0%	2
59531	Liberty County 73.0% Hill County 27.0%	27.0%	2
59540	Hill County 96.1% Chouteau County 3.9%	3.9%	2
59542	Blaine County 65.3% Phillips County 34.7%	34.7%	2
59545	Liberty County 68.1% Toole County 31.9%	31.9%	2
59635	Lewis and Clark County 38.1% Jefferson County 36.2% Broadwater County 25.8%	61.9%	3
59645	Meagher County 98.6% Broadwater County 1.4%	1.4%	2
59701	Silver Bow County 48.6% Jefferson County 46.8% Deer Lodge County 4.6%	51.4%	3
59711	Deer Lodge County 63.6% Granite County 25.5% Silver Bow County 11.0%	36.4%	3
59715	Gallatin County 91.8% Park County 8.2%	8.2%	2
59716	Madison County 55.8% Gallatin County 44.2%	44.2%	2
59721	Jefferson County 61.6% Madison County 38.4%	38.4%	2
59722	Powell County 85.7% Deer Lodge County 14.3%	14.3%	2
59725	Beaverhead County 96.0% Madison County 4.0%	4.0%	2
59727	Silver Bow County 79.6% Beaverhead County 20.4%	20.4%	2
59730	Gallatin County 94.1% Madison County 5.9%	5.9%	2
59732	Beaverhead County 58.4% Madison County 41.6%	41.6%	2
59743	Beaverhead County 62.7% Madison County 27.9% Silver Bow County 9.4%	37.3%	3
59752	Gallatin County 62.0% Jefferson County 19.6% Broadwater County 18.4%	38.0%	3
59759	Jefferson County 61.2% Madison County 32.3% Silver Bow County 6.5%	38.8%	3
59762	Deer Lodge County 56.0% Beaverhead County 44.0%	44.0%	2
59820	Mineral County 72.1% Missoula County 27.9%	27.9%	2
59821	Missoula County 43.9% Lake County 37.3% Sanders County 18.9%	56.1%	3
59825	Granite County 61.7% Missoula County 38.3%	38.3%	2
59833	Ravalli County 70.2% Missoula County 29.8%	29.8%	2
59845	Sanders County 66.9% Lake County 17.4% Flathead County 15.7%	33.1%	3
59847	Missoula County 94.8% Idaho County, ID 5.2%	5.2%	2
59866	Mineral County 90.6% Sanders County 9.4%	9.4%	2
59868	Missoula County 95.7% Powell County 4.3%	4.3%	2
59911	Lake County 85.6% Flathead County 14.4%	14.4%	2
59922	Flathead County 89.9% Lake County 10.1%	10.1%	2
82801	Sheridan County, WY 97.4% Big Horn County 2.6%	2.6%	2

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.

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