Nassau County
Nassau County is a county located in the U.S. state of Florida. It is the northeasternmost county in the state. The county seat is Fernandina Beach. The population was 90,352 at the 2020 census. Nassau County is a constituent of the Jacksonville, Florida Metropolitan Statistical Area, which accommodates around 1.68 million inhabitants as of 2022.

Duval County
Duval County, officially the City of Jacksonville and Duval County, is a county in the northeastern part of the U.S. state of Florida. As of the 2020 census, its population was 995,567, making it the sixth-most populous county in Florida. Its county seat is Jacksonville, with which the Duval County government has been consolidated since 1968.

Baker County
Baker County is a county in the U.S. state of Florida. As of the 2020 census, the population was 28,259. Its county seat is Macclenny. The county was founded in 1861 and is named for James McNair Baker, a judge and Confederate Senator. Baker County is included in the Jacksonville metropolitan area.

Leon County
Leon County is a county in the Panhandle of the U.S. state of Florida. It was named after the Spanish explorer Juan Ponce de León. As of the 2020 census, the population was 292,198. The county seat is Tallahassee, which is also the state capital and home to many politicians, lobbyists, jurists, and attorneys. Leon County is included in the Tallahassee, Florida Metropolitan Statistical Area.

Marion County
Marion County is a county located in the North Central region of the U.S. state of Florida. As of the 2020 United States census, the population was 375,908. Its county seat is Ocala. Marion County comprises the Ocala, Florida Metropolitan Statistical Area. It includes part of Ocala National Forest, which also extends into three other counties.

Alachua County
Alachua County is a county in the north central portion of the U.S. state of Florida. As of the 2020 census, the population was 278,468. The county seat is Gainesville, the home of the University of Florida. Artifacts from the Archaic period (8000 – 2000 BC) have been found at several sites in Alachua County.

Union County
Union County is a county located in the north central portion of the U.S. state of Florida, the smallest in the state by area. As of the 2020 census, the population was 16,147. The county seat is Lake Butler. Union County was created on October 1, 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.

Columbia County
Columbia County is a county located in the north central portion of the U.S. state of Florida. As of the 2020 census, the population was 69,698, up from 67,531 at the 2010 census. Its county seat is Lake City. Columbia County comprises the Lake City, FL Micropolitan Statistical Area, which is included in the Gainesville-Lake City, FL Combined Statistical Area.

Bradford County
Bradford County is a county in the north central region of the U.S. state of Florida. As of the 2020 census, the population was 28,303. Its county seat and largest city is Starke. Bradford County does not have any interstate connections; the nearest connection is with I-75 to the west of the county.

Flagler County
Flagler County is a county located in the northeastern portion of the U.S. state of Florida. As of the 2020 census, the population was 115,378. Its county seat is Bunnell, and the largest city is Palm Coast. Created in 1917 from portions of Saint Johns and Volusia Counties, it was named for Henry Flagler, who built the Florida East Coast Railway.

Putnam County
Putnam County is a county located in the northern part of the state of Florida. As of the 2020 census, the population was 73,321. Its county seat is Palatka. Putnam County comprises the Palatka, Florida Micropolitan Statistical Area, which is included in the Jacksonville—Kingsland—Palatka, Florida—Georgia Combined Statistical Area and is located between Jacksonville, Gainesville, St. Augustine, and Daytona Beach.

Clay County
Clay County is a county located in the northeastern part of the U.S. state of Florida along the west bank of the St. Johns River. As of 2020, the population was 218,245 and in 2023, that number increased to 232,439, making it the third largest county in the Jacksonville metropolitan area.

Saint Johns County
St. Johns County is a county in the northeastern part of the U.S. state of Florida. As of the 2020 United States census, its population was 273,425. The county seat and most populous incorporated city is St. Augustine, although the nearby community, St. Johns, has a higher population. St. Johns County is part of the Jacksonville, Florida Metropolitan Statistical Area.