Tuscaloosa is a city in and the county seat of Tuscaloosa County in west-central Alabama, United States, on the Black Warrior River where the Gulf Coastal and Piedmont plains meet. Alabama's fifth-most populous city, the population was 99,600 at the 2020 census, and was estimated to be 111,338 in 2023. It was known as Tuskaloosa until the early 20th century. It is also known as "the Druid City" because of the numerous water oaks planted in its downtown streets since the 1840s.