Newberry Library: Atlas of Historical County Boundaries Project

Newberry Library: Atlas of Historical County Boundaries Project

Interactive maps, downloadable shapefiles, and chronological narratives of state and county boundaries over time. Useful for historical and genealogical research.

Massachusetts' chronology is particularly interesting, as it covers the former separate colony of Plymouth and the Maine and New Hampshire regions that were split off as separate entities. I'd always wondered why Norfolk County is south of Suffolk. Unfortunately, the Oklahoma data set treats Indian Territory as a unitary entity, rather than attending to the changes in tribal boundaries over the course of the 19th century.

(Via a Center for Investigative Reports article about how they used satellite imagery and boundary information to trace out the U. S. / Mexico border fence. They used OpenStreetMap and JOSM to create a shapefile of the fence.)