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ZIP codes and county lines / MD

ZIP codes and county lines in Maryland

82 of the 478 ZIP code areas in Maryland, or 17.2%, 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
478

Census ZCTAs with any land in Maryland

In more than one county
82

17.2% of the state, against 30.1% nationally

At least 5% in a second county
59

12.3% of the state, more than a sliver

Cross a state line
3

Into Delaware

How Maryland compares

Maryland ranks 35 of 52 (the 50 states, DC and Puerto Rico) by the share of its ZIP code areas that overlap more than one county. 24 of its counties have at least one split ZIP code area along an edge. 3 of its ZIP code areas also reach into Delaware, so a ZIP list that is meant to stop at the state line does not.

Counties with the most split ZIP code areas

  1. Baltimore County: 29 ZIP codes shared with another county
  2. Baltimore city: 18 ZIP codes shared with another county
  3. Carroll County: 12 ZIP codes shared with another county
  4. Frederick County: 12 ZIP codes shared with another county
  5. Howard County: 11 ZIP codes shared with another county

Every split ZIP code area in Maryland

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
19973
  • Sussex County, DE 92.7%
  • Dorchester County 7.3%
7.3%2
20601
  • Charles County 83.9%
  • Prince George's County 16.1%
16.1%2
20607
  • Prince George's County 96.4%
  • Charles County 3.6%
3.6%2
20613
  • Prince George's County 91.7%
  • Charles County 8.3%
8.3%2
20622
  • Charles County 83.3%
  • St. Mary's County 16.7%
16.7%2
20659
  • St. Mary's County 95.9%
  • Charles County 4.1%
4.1%2
20701
  • Howard County 54.1%
  • Anne Arundel County 45.9%
45.9%2
20705
  • Prince George's County 98.9%
  • Montgomery County 1.1%
1.1%2
20707
  • Prince George's County 93.8%
  • Montgomery County 6.2%
6.2%2
20714
  • Anne Arundel County 64.2%
  • Calvert County 35.8%
35.8%2
20736
  • Calvert County 97.0%
  • Anne Arundel County 3.0%
3.0%2
20754
  • Calvert County 83.1%
  • Anne Arundel County 16.9%
16.9%2
20758
  • Anne Arundel County 97.5%
  • Calvert County 2.5%
2.5%2
20777
  • Howard County 98.3%
  • Montgomery County 1.7%
1.7%2
20794
  • Howard County 66.5%
  • Anne Arundel County 33.5%
33.5%2
20833
  • Montgomery County 90.2%
  • Howard County 9.8%
9.8%2
20842
  • Montgomery County 77.5%
  • Frederick County 22.5%
22.5%2
20871
  • Montgomery County 94.4%
  • Frederick County 5.6%
5.6%2
20903
  • Montgomery County 95.1%
  • Prince George's County 4.9%
4.9%2
20904
  • Montgomery County 97.5%
  • Prince George's County 2.5%
2.5%2
20912
  • Montgomery County 90.0%
  • Prince George's County 10.0%
10.0%2
21013
  • Baltimore County 71.1%
  • Harford County 28.9%
28.9%2
21043
  • Howard County 96.8%
  • Baltimore County 3.2%
3.2%2
21074
  • Carroll County 72.0%
  • Baltimore County 28.0%
28.0%2
21076
  • Anne Arundel County 89.7%
  • Howard County 10.3%
10.3%2
21082
  • Baltimore County 97.4%
  • Harford County 2.6%
2.6%2
21085
  • Harford County 94.3%
  • Baltimore County 5.7%
5.7%2
21087
  • Baltimore County 90.1%
  • Harford County 9.9%
9.9%2
21102
  • Carroll County 76.7%
  • Baltimore County 23.3%
23.3%2
21104
  • Howard County 53.5%
  • Carroll County 31.9%
  • Baltimore County 14.7%
46.5%3
21111
  • Baltimore County 76.7%
  • Harford County 23.3%
23.3%2
21136
  • Baltimore County 96.2%
  • Carroll County 3.8%
3.8%2
21155
  • Baltimore County 89.1%
  • Carroll County 10.9%
10.9%2
21161
  • Harford County 53.2%
  • Baltimore County 46.8%
46.8%2
21163
  • Baltimore County 73.3%
  • Howard County 26.7%
26.7%2
21206
  • Baltimore city 68.7%
  • Baltimore County 31.3%
31.3%2
21207
  • Baltimore County 72.0%
  • Baltimore city 28.0%
28.0%2
21208
  • Baltimore County 98.6%
  • Baltimore city 1.4%
1.4%2
21209
  • Baltimore County 55.6%
  • Baltimore city 44.4%
44.4%2
21210
  • Baltimore city 84.4%
  • Baltimore County 15.6%
15.6%2
21212
  • Baltimore city 56.6%
  • Baltimore County 43.4%
43.4%2
21215
  • Baltimore city 96.5%
  • Baltimore County 3.5%
3.5%2
21222
  • Baltimore County 93.5%
  • Baltimore city 6.5%
6.5%2
21224
  • Baltimore city 72.6%
  • Baltimore County 27.4%
27.4%2
21225
  • Anne Arundel County 64.4%
  • Baltimore city 35.6%
35.6%2
21226
  • Baltimore city 50.2%
  • Anne Arundel County 49.8%
49.8%2
21227
  • Baltimore County 96.7%
  • Baltimore city 3.3%
3.3%2
21228
  • Baltimore County 99.9%
  • Baltimore city 0.1%
0.1%2
21229
  • Baltimore city 85.6%
  • Baltimore County 14.4%
14.4%2
21234
  • Baltimore County 92.7%
  • Baltimore city 7.3%
7.3%2
21236
  • Baltimore County 98.1%
  • Baltimore city 1.9%
1.9%2
21237
  • Baltimore County 93.7%
  • Baltimore city 6.3%
6.3%2
21239
  • Baltimore city 73.3%
  • Baltimore County 26.7%
26.7%2
21521
  • Garrett County 62.2%
  • Allegany County 37.8%
37.8%2
21532
  • Allegany County 54.5%
  • Garrett County 45.5%
45.5%2
21539
  • Garrett County 57.4%
  • Allegany County 42.6%
42.6%2
21562
  • Garrett County 50.3%
  • Allegany County 49.8%
49.8%2
21620
  • Kent County 74.3%
  • Queen Anne's County 25.7%
25.7%2
21632
  • Caroline County 79.8%
  • Dorchester County 20.2%
20.2%2
21640
  • Caroline County 80.2%
  • Queen Anne's County 19.8%
19.8%2
21649
  • Queen Anne's County 52.3%
  • Caroline County 47.7%
47.7%2
21651
  • Kent County 70.6%
  • Queen Anne's County 29.4%
29.4%2
21655
  • Caroline County 100.0%
  • Dorchester County under 0.1%
under 0.1%2
21657
  • Queen Anne's County 76.7%
  • Talbot County 19.9%
  • Caroline County 3.4%
23.3%3
21679
  • Talbot County 96.7%
  • Queen Anne's County 3.3%
3.3%2
21719
  • Washington County 97.4%
  • Frederick County 2.6%
2.6%2
21757
  • Carroll County 52.4%
  • Frederick County 47.6%
47.6%2
21758
  • Frederick County 50.3%
  • Washington County 49.7%
49.7%2
21769
  • Frederick County 99.3%
  • Washington County 0.7%
0.7%2
21771
  • Frederick County 51.4%
  • Carroll County 26.2%
  • Howard County 18.2%
  • Montgomery County 4.2%
48.6%4
21776
  • Carroll County 79.2%
  • Frederick County 20.8%
20.8%2
21780
  • Frederick County 95.7%
  • Washington County 4.3%
4.3%2
21783
  • Washington County 72.9%
  • Frederick County 27.1%
27.1%2
21784
  • Carroll County 82.0%
  • Howard County 18.0%
18.0%2
21787
  • Carroll County 87.0%
  • Frederick County 13.0%
13.0%2
21791
  • Frederick County 60.7%
  • Carroll County 39.3%
39.3%2
21797
  • Howard County 66.9%
  • Carroll County 31.8%
  • Montgomery County 1.3%
33.1%3
21804
  • Wicomico County 77.6%
  • Worcester County 22.4%
22.4%2
21822
  • Wicomico County 49.9%
  • Worcester County 26.5%
  • Somerset County 23.6%
50.1%3
21851
  • Worcester County 80.3%
  • Somerset County 19.6%
19.6%2
21874
  • Wicomico County 99.5%
  • Sussex County, DE 0.5%
0.5%2
21912
  • Cecil County 99.8%
  • New Castle County, DE 0.2%
0.2%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.

Route by the boundary, not the ZIP

MapLogics decides who owns an address from a boundary you draw or import, so a ZIP that straddles two counties is answered by where the address actually is. There is a free trial if you want to see it on your own addresses.

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