“Beginning in the 1850s, entrepreneurs initiated an important phase in the history of American cartography by producing very detailed maps of counties. Often called ‘land ownership maps’ because they indicate the farms and residences of subscribers, these were usually the first maps of most counties in the Northeast and Midwest, and the Great Plains states. In addition to showing land owners throughout the county, they often contain inset maps of towns and villages as well as vignettes of residences, businesses, and farms. County land ownership maps are among the most heavily used materials in the division [Geography & Maps] because of their value to genealogical studies. The Titled Collection contains nearly fifteen hundred such maps published before 1900, which are described in ‘Land Ownership Maps: A Checklist of Nineteenth-Century United States County Maps in the Library of Congress (Washington, 1967)’.”
These maps have been digitized (Ancestry.com collection “Indexed County Land Ownership Maps, 1860-1918”) and are also available on microfiche. The Newberry has a set of the microfich (Call No. Microfiche 583) as well as a copy of the Checklist (Call No. Local History Ref Z6027.U5 U54 )
For more information, check out the Library of Congress page on Land Owership Maps and Atlases.