Princeton is a city in and the county seat of Mercer County, West Virginia, United States. The population was 5,872 at the 2020 census. It is par…Princeton is a city in and the county seat of Mercer County, West Virginia, United States. The population was 5,872 at the 2020 census. It is part of the Bluefield micropolitan area. The city hosts the Princeton WhistlePigs baseball club of the Appalachian League.