About

Additional detail about the project is also available by visiting the About pages for individual states.

Credits

Thanks to The Newberry, in Chicago, Ill., for permission to use Atlas of Historical County Boundaries data in this resource, which will be incorporated in a future version.

Cover Art: Hamlin, Homer. Map showing territory annexed to the city of Los Angeles, California. [Los Angeles, Calif.:] City Engineer, 1916. https://hdl.loc.gov/loc.gmd/g4364l.ct001800.

Map Icons: Derived from 2 Natural Earth datasets (Version 5.0.0): 1:10m Cultural Vectors, Admin 1 – States, Provinces (without large lakes) and 1:50m Cultural Vectors, Admin 0 – Countries (without boundary lakes).

Priorities

Like many projects of this scale, the vast amount of knowledge to be uncovered often exceeds the resources available. The following priorities generally decide what information is included:

Geohistory events for incorporated places, such as boroughs, cities, and villages, are prioritized over those for townships and other county subdivisions.
Incorporations, name changes, consolidations, mergers, disincorporations, and substantial government form change events are prioritized over annexations. In turn, annexations are prioritized over minor boundary adjustments and disputed boundary determinations.
Modern geohistory events, particularly since 1900, are prioritized over older geohistory events, which are often chronicled in preexisting county histories.
Identifying geohistory events and cataloging primary source citations is prioritized over GIS efforts.