ZIP codes and county lines / CT
ZIP codes and county lines in Connecticut
11 of the 288 ZIP code areas in Connecticut, or 3.8%, 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
- 288
- In more than one county
- 11
- At least 5% in a second county
- 3
- Cross a state line
- 0
Census ZCTAs with any land in Connecticut
3.8% of the state, against 30.1% nationally
1.0% of the state, more than a sliver
None reach another state
How Connecticut compares
Connecticut ranks 49 of 52 (the 50 states, DC and Puerto Rico) by the share of its ZIP code areas that overlap more than one county. 8 of its counties have at least one split ZIP code area along an edge.
Counties with the most split ZIP code areas
- Windham County: 6 ZIP codes shared with another county
- New London County: 5 ZIP codes shared with another county
- Tolland County: 3 ZIP codes shared with another county
- Hartford County: 2 ZIP codes shared with another county
- Litchfield County: 2 ZIP codes shared with another county
Every split ZIP code area in Connecticut
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 | |||
|---|---|---|---|
| 06065 | 23.9% | 2 | |
| 06226 | 2.2% | 2 | |
| 06242 | 3.0% | 2 | |
| 06250 | 0.7% | 2 | |
| 06330 | 25.1% | 2 | |
| 06331 | under 0.1% | 2 | |
| 06384 | 0.1% | 2 | |
| 06415 | 12.5% | 2 | |
| 06420 | 2.1% | 2 | |
| 06451 | 0.2% | 2 | |
| 06784 | 0.3% | 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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