Substantial county boundary changes are those affecting an estimated population of 200 or more; changes of at least one square mile where an estimated population number was not available, but research indicated that 200 or more people may have been affected; and annexations of unpopulated territory of at least 10 square miles.
The Census Bureau’s reference date for geographic entity boundaries in all geographic and statistical data products is January 1 of the reference year (e.g., January 1, 2019). Boundary changes with effective dates after January 1 will appear in geographic and statistical data products referenced to the following year. For example, a change with an effective date of January 2, 2019 will appear in products referenced to 2020.
Changes are listed below in the decade they occurred.
The Census Bureau does not produce before-and-after maps illustrating the boundary changes. Contact the state or county governments for more specific information about these changes.