Deer Park is a city in Hamilton County, Ohio, United States. It is a suburb of Cincinnati. The population was 5,432 at the 2020 census. The Cincinnati, Lebanon and Northern Railway began running through the town in 1881, along the "Highland Route". In 1795, following the signing of the Treaty of Greenville which provided assurances to Ohio settlers that they would be protected from Indian "intrusions", Samuel and Rebecca DeMent Pierson established the first log home in the area near Deer Park.