Carroll County is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 172,891. Its county seat is Westminster. Carroll County is included in the Baltimore-Columbia-Towson, MD Metropolitan Statistical Area, which is also included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. …Carroll County is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 172,891. Its county seat is Westminster. Carroll County is included in the Baltimore-Columbia-Towson, MD Metropolitan Statistical Area, which is also included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. While predominantly rural, the county has become increasingly suburban in recent years.