Hillsboro
- County:
- Jefferson County
- County Seat:
- Yes
- Area (mi²):
- 3.842
- State:
- Missouri
Hillsboro is a city located in Jefferson County, Missouri. Hillsboro has a 2026 population of 3,489. It is also the county seat of Jefferson County. Hillsboro is currently declining at a rate of -0.37% annually and its population has decreased by 0% since the most recent census, which recorded a population of 3,489 in 2020.