Hillsboro is a city in Jefferson County, Missouri, United States. The estimated population as of 2008 is 2,062. The population was 1,675 at the 2000 census. It is the county seat of Jefferson County.
Hillsboro is the English equivalent of the Italian Monticello, home of President Thomas Jefferson. The founders of Jefferson County had hoped to use the name of the home of their county's namesake for the county seat, but that honor in Missouri had already been taken by Monticello in Lewis County.
Hillsboro is located at 38°13′56″N 90°33′48″W / 38.23222°N 90.56333°W / 38.23222; -90.56333 (38.232346, -90.563233). According to the United States Census Bureau, the city has a total area of 2.4 square miles (6.2 km²), all of it land.