How County Boundary Changes Affect FIPS Codes

County FIPS codes are generally stable, but they do change when counties are created, dissolved, renamed, or renumbered. The Census Bureau maintains a vintage-specific reference list and publishes change notes when codes are updated. For most analysts working with recent data, these changes are rare enough to ignore — but for anyone building long-run historical datasets, code changes can silently break joins.

Notable recent changes: Shannon County, SD → Oglala Lakota County (2015) — renamed and renumbered from 46113 to 46102. Bedford City, VA → Bedford County (2013) — the independent city was merged into the county; its separate FIPS code (51515) was eliminated and its geography absorbed into Bedford County (51019). Wade Hampton Census Area, AK → Kusilvak Census Area (2015) — renamed and renumbered from 02270 to 02158. Connecticut reorganization (2022) — 8 counties replaced by 9 planning regions with entirely new codes.

There have also been code changes in Virginia, where independent cities have occasionally merged with surrounding counties. Virginia has the most complex county-equivalent geography in the US because of its 38 independent cities (which are county-equivalents but separate from the counties around them). Any analysis of Virginia that spans boundary change years needs careful handling.

The best practice for handling code changes in long-run datasets is to use the Census Bureau's "vintage-specific" reference files — these document exactly which codes were active in which years. For current data, our county FIPS reference and individual county pages like King County (53033) reflect the current authoritative list. The search tool is useful for quickly verifying whether a code is current.