Middleburg is an unincorporated area and census-designated place located in the U.S. state of Florida. It is within Clay County approximately 26 miles in southwest Jacksonville. It has a total area of 19.6 square miles at 30°3′3″N 81°54′7″W. The elevation is 33 feet above sea level. As of the 2010 census data, it had a total population of 13,008. The population density was 665/sq mi. Estimated per capita income in 2016 was $20,945. Recent job growth is positively increased by 2.08 percent. The average travel time is 40 minutes. It has Zip codes 32050 and 32068.