The Matanzas River is a body of water in St. Johns and Flagler counties in the U.S. state of Florida. It is a narrow saltwater bar-bounded estuary sheltered from the Atlantic Ocean by Anastasia Island. The river is part of the Atlantic Intracoastal Waterway.

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.