Gillette is a city in and the county seat of Campbell County, Wyoming, United States. The town was founded in 1891 as a major railway town on the Chicago, Burlington and Quincy Railroad. The population was estimated at 33,496, as of July 1, 2023, making it the 3rd most populous city in Wyoming after Cheyenne and Casper. Gillette's population increased 48% in the ten years after the 2000 census, which counted 19,646 residents after a boom in its local fossil fuel industries.