The homepage of the Atlas of Historical County Boundaries has (at the bottom right hand corner) animated the historical development of county, state and territorial boundary lines!
You can select Massachusetts (or any state), and will have use of all these features for each state:
- Interactive map allows you to select a date & view county boundaries on that date (Mass begins w/ 1629).
- The Consolidated Chronology lists everything that has happened to all Mass. county boundaries from 1606 to 1947.
- Individual County Chronologies groups events from each county's boundary history from the Consolidated Chronology.
- Bibliography of sources lists the primary and secondary sources found useful in the historical research of territorial, state, and county boundaries.
And there are other features available to explore on the website.