Mason is a city in southwestern Warren County, Ohio, United States, approximately 22 miles (35 km) north of downtown Cincinnati. As of the 2020 census, Mason's population was 34,792. It is home to Kings Island amusement park and one of the largest tennis stadiums in the world, the Lindner Family Tennis Center, home of the Cincinnati Open, one of the world's top tennis tournaments for both men and women.

Warren County is a county located in the southwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 242,337. Its county seat is Lebanon and largest city is Mason. The county is one of Ohio's most affluent, with the highest median income of the state's 88 counties. The county was established on May 1, 1803, from Hamilton County; it is named for Dr. Joseph Warren, a hero of the Revolution who sent Paul Revere and the overlooked William Dawes on their famous rides and who died at the Battle of Bunker Hill. Warren County is part of the Cincinnati, OH-KY-IN Metropolitan Statistical Area.