Pittsfield is the most populous city in and the county seat of Berkshire County, Massachusetts, United States. It is the principal city of the Pittsfield, Massachusetts Metropolitan Statistical Area, which encompasses Berkshire County. Pittsfield's population was 43,927 at the 2020 census. Although its population has declined in recent decades, Pittsfield remains the third-largest municipality in Western Massachusetts, behind only Springfield and Chicopee.