US Census Bureau - Population Estimates Data Sets

Added By Infochimps

[From the site]

Datasets for all geographies

Datasets are provided here to download for analysis in spreadsheet, statistical, or geographic information systems software. Files are in fixed-length ASCII format, each with a separate layout file, and in .csv, a generic spreadsheet format. Files include Federal Information Processing System (FIPS) codes, which uniquely identify geographic areas.