Hillsboro is a city in Montgomery County, Illinois, United States. The population was 4,359 at the 2000 census, and 6,106 at a 2009 estimate. It is the county seat of Montgomery County.
Hillsboro was given its name because one of the first settling families' names was "Hillsborough".
The Evangelical Lutheran Synod of Illinois held its first convention in Hillsboro, October 15, 1846.