Zip Code Population by County

As a standard disclaimer, this data uses Zip Code Tabulation Areas (ZCTAs) which are technically different than ZIP codes. In some cases this difference doesn't matter, sometimes it's significant, often ZCTAs are the best you can do regardless. ZIP codes don't technically exist as geographies (they're discretely assigned to each address based on post offices and delivery routes), but since we all think of them as geographies, the Census created ZCTAs to approximate the boundaries of addresses in a given ZIP code. Usually, ZCTAs are very close to the actual on-the-ground ZIP codes, but it's uneven. ZCTAs are only updated every 10 years, so right now, they're better than they'll be in 2029. Areas with fast growth (or decline) are most likely to have changes to their ZIP codes, making ZCTA boundaries less accurate. Depending on the precision you need for what you're doing, this could be a non-issue or a showstopper.

As a standard disclaimer, this data uses Zip Code Tabulation Areas (ZCTAs) which are technically different than ZIP codes. In some cases this difference doesn't matter, sometimes it's significant, often ZCTAs are the best you can do regardless. ZIP codes don't technically exist as geographies (they're discretely assigned to each address based on post offices and delivery routes), but since we all think of them as geographies, the Census created ZCTAs to approximate the boundaries of addresses in a given ZIP code. Usually, ZCTAs are very close to the actual on-the-ground ZIP codes, but it's uneven. ZCTAs are only updated every 10 years, so right now, they're better than they'll be in 2029. Areas with fast growth (or decline) are most likely to have changes to their ZIP codes, making ZCTA boundaries less accurate. Depending on the precision you need for what you're doing, this could be a non-issue or a showstopper.

One major difference between ZCTAs and ZIP codes is that houses on either side of a street will usually be in the same ZIP code, but they could be in different ZCTAs, because block boundaries run down the middle of streets.

Dear Bernie,

Just as a conceptual issue, addresses (via the master address file) are also used for block groups.  In theory you could set up a "correlation" between the census master address file and the post office file. https://geocoding.geo.census.gov/geocoder/geographies/onelineaddress?form  Glenn, I sure you know more about this than I do.  Does geocorr use the actual addresses or just the Tiger polygons with the longitude and latitude ?

Neither. I use the 2020 ZCTA to Census Tabulation Block Relationship File (https://www2.census.gov/geo/docs/maps-data/data/rel2020/zcta520/tab20_zcta520_tabblock20_natl.txt -- but don't click the link, it's a very large file). The Geocorr database (aka MABLE) is just a list of blocks with every block assigned to one and only one ZCTA (and the other larger geography types).