An act approved by the Wisconsin Territorial Legislature on December 21, 1837 established boundaries for the county lying west of Delaware County and running to the western edge of the territory at the Missouri River. The county was in all other respects a part of Dubuque County, but this was the first step towards the growth of a new county, Buchanan County. It is said that S. P. Stoughton, a strong Democrat, suggested naming the county after Senator James Buchanan, for Buchanan was instrumental in the acquisition of the Wisconsin Territory. In 1843 the county was reduced to its present limits of 571 square miles or 365,627 acres.