Marlin is a city in Falls County, Texas, United States. Its population was 5,462 at the 2020 census. Since 1851, it has been the county seat of Falls County. Marlin has been given the nickname "The Hot Mineral Water City of Texas" by the 76th Texas State Legislature. Mineral water was discovered there in 1892.

Falls County is a county in the U.S. state of Texas. As of the 2020 census, its population was 16,968. The county seat is Marlin. It is named for the original 10-foot-tall waterfall on the Brazos River, which existed until the river changed course during a storm in 1866. The present falls is two miles northeast of the original falls, at the Falls on the Brazos Park, a camping site only a few miles out of Marlin on Farm to Market Road 712.