Metropolitan Statistical Areas: Understanding MSA FIPS Codes

Metropolitan Statistical Areas (MSAs) are geographic units defined by the Office of Management and Budget (OMB) to represent integrated economic regions centered on urban cores. Each MSA has a 5-digit CBSA (Core Based Statistical Area) code — commonly called the MSA FIPS code — used by the BLS, Census Bureau, HUD, and other agencies to publish economic and demographic data at the metro level.

There are three types of Core Based Statistical Areas: Metropolitan Statistical Areas (population ≥50,000), Micropolitan Statistical Areas (population 10,000–49,999), and Combined Statistical Areas (groups of adjacent CBSAs with strong commuting ties). Each has its own 5-digit code. The Seattle-Tacoma-Bellevue MSA (42660) is a Metropolitan Statistical Area; smaller cities have Micropolitan designations. You can browse all MSAs and their component counties on their individual pages.

MSA boundaries are reviewed and revised by OMB after each decennial census, which means the component counties of an MSA can change. The 2023 OMB delineation (used by this site) is the current standard. When working with older datasets, verify which delineation year was used — a county that was in an MSA under 2013 standards may not be under 2023 standards.

For data analysis, the key thing to understand is that MSA FIPS codes and county FIPS codes are two different geographic layers. An MSA code identifies the entire metro region; to get county-level data for a metro, you need the list of component counties. Our MSA pages, like the one for Seattle (42660), show exactly which counties are included, which are central vs. outlying, and which federal datasets publish at the MSA level.