Geometries of the features in the data sets (the administrative units) were adopted from data provided by the Census Mosaic Project, http://www.censusmosaic.org/. A county borders data set was created by merging the features provided, editing them where necessary (using additional spatial data) and adding attribute information, such as county name. Attributes of the features were then compared to data provided by literature as well as the HGIS Germany Project, a cooperation between the Leibniz Institute of European History (IEG) and the Institute for Spatial Information and Surveying Technology (i3mainz) of the University of Applied Sciences, Mainz, http://www.hgis-germany.de/. HGIS data sets are available for download from the Harvard Geospatial Library (HGL) in conjunction with OpenGeoportal from https://geodata.lib.berkeley.edu/ Antonia Dückelmann and Peter Paul Marckhgott-Sanabria were responsible for reviewing the existing, provided data sets, for data consolidation and harmonization, and for data editing. Peter Paul Marckhgott-Sanabria was responsible for historical investigation and validation, in particular for reviewing the created data sets, for data harmonization and for research on administrative structures in the time period and on the dates of existence of the respective administrative units (time spans between formation and disintegration).