Union County is a county located in the state of Florida, the smallest in the state. As of the 2010 census, the population was 15,535. The county seat is Lake Butler.HistoryUnion County was created in 1921 from part of Bradford County. It was named to honor the concept of unity. Union County is the location of Union Correctional Institution and the Reception and Medical Center (RMC). Union CI is a maximum security prison and is home to part of Florida's Death Row. The death chamber is located at nearby Florida State Prison (FSP). Florida State Prison also houses some death-row inmates.GeographyAccording to the U.S. Census Bureau, the county has a total area of, of which is land and (2.5%) is water. It is the smallest county by area in Florida.Adjacent countiesBradford County, Florida - southeastAlachua County, Florida - southColumbia County, Florida - westBaker County, Florida - north