Carlisle is a borough in and the county seat of Cumberland County, Pennsylvania, United States. Carlisle is located within the Cumberland Valley, a highly productive agricultural region. As of the 2020 census, the borough population was 20,118; including suburbs in the neighboring townships, 37,695 live in the Carlisle urban cluster. Carlisle is the smaller principal city of the Harrisburg–Carlisle metropolitan statistical area, which includes Cumberland and Dauphin and Perry counties in South Central Pennsylvania.