Hillsboro
- County:
- Montgomery County
- County Seat:
- Yes
- Area (mi²):
- 8.628
- State:
- Illinois
Hillsboro is a city located in Montgomery County, Illinois. Hillsboro has a 2026 population of 5,761. It is also the county seat of Montgomery County. Hillsboro is currently declining at a rate of -0.38% annually and its population has decreased by -1.71% since the most recent census, which recorded a population of 5,861 in 2020.