Jo Daviess County is a county located in the northwest corner of U.S. state of Illinois. According to the 2010 census, it had a population of 22,678, which is an increase of 1.7% from 22,289 in 2000. Its county seat is Galena.

As part of the Driftless Area, Jo Daviess County is known for its scenic stretches of road and valley views. Within Jo Daviess County lies Charles Mound, the highest natural point in Illinois.

Jo Daviess County is part of the Tri-State Area and the Dubuque, Iowa, Galena, Illinois, Platteville, Wisconsin, metropolitan area.

Jo Daviess County was formed in 1827 out of Henry and Putnam Counties. It is named for Maj. Joseph Hamilton Daveiss, United States District Attorney for Kentucky, who was killed in 1811 at the Battle of Tippecanoe. Maj. Daveiss’ name is universally misspelled, as in the name of this and other counties. The local pronunciation is “Davis”.

A proposed wind farm would be located near the town of Nora in the northeastern corner of the county.