http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Historical atlas and chronology of county boundaries, 1788-1980
Hermon Dunlap Smith Center for the History of Cartography
V. 1. Delaware, Maryland, New Jersey, Pennsylvania. -- v. 2. Illinois, Indiana, Ohio. -- v. 3. Michigan, Wisconsin. -- v. 4. Iowa, Missouri. -- v. 5. Minnesota, North Dakota, South Dakota.
County maps published at the scale of 1:625,000.