Middleburg is an unincorporated area and census-designated place (CDP) within Clay County, Florida, United States, located 26 miles (42 km) southwest of downtown Jacksonville and 16 miles (26 km) northwest of Green Cove Springs, the Clay County seat. It is home to Middleburg High School. As of the 2010 census, the population of Middleburg was 13,008. Median household income is $56,818.
