ZIP codes and county lines in Alaska

12 of the 245 ZIP code areas in Alaska, or 4.9%, 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: 245
In more than one county: 12
At least 5% in a second county: 11
Cross a state line: 0

How Alaska compares

Alaska ranks 46 of 52 (the 50 states, DC and Puerto Rico) by the share of its ZIP code areas that overlap more than one county. 15 of its counties have at least one split ZIP code area along an edge.

Counties with the most split ZIP code areas

Copper River Census Area: 3 ZIP codes shared with another county
Southeast Fairbanks Census Area: 3 ZIP codes shared with another county
Yukon-Koyukuk Census Area: 3 ZIP codes shared with another county
Denali Borough: 2 ZIP codes shared with another county
Fairbanks North Star Borough: 2 ZIP codes shared with another county

Every split ZIP code area in Alaska

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
99503	Bethel Census Area 83.7% Anchorage Municipality 16.3%	16.3%	2
99588	Copper River Census Area 55.9% Matanuska-Susitna Borough 44.1%	44.1%	2
99613	Lake and Peninsula Borough 81.6% Bristol Bay Borough 18.4%	18.4%	2
99701	Yukon-Koyukuk Census Area 97.4% Fairbanks North Star Borough 2.6%	2.6%	2
99729	Matanuska-Susitna Borough 89.4% Denali Borough 10.6%	10.6%	2
99737	Southeast Fairbanks Census Area 76.2% Copper River Census Area 23.8%	23.8%	2
99738	Southeast Fairbanks Census Area 58.4% Yukon-Koyukuk Census Area 41.6%	41.6%	2
99760	Yukon-Koyukuk Census Area 55.6% Denali Borough 43.3% Fairbanks North Star Borough 1.1%	44.4%	3
99780	Southeast Fairbanks Census Area 94.7% Copper River Census Area 5.3%	5.3%	2
99827	Haines Borough 55.4% Hoonah-Angoon Census Area 44.6%	44.6%	2
99833	Petersburg Borough 65.1% Prince of Wales-Hyder Census Area 34.9%	34.9%	2
99901	Ketchikan Gateway Borough 86.5% Prince of Wales-Hyder Census Area 13.5%	13.5%	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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