Anne Arundel County, also notated as AA or A.A. County, is a county located in the U.S. state of Maryland. As of the 2020 United States census, its population was 588,261, an increase of just under 10% since 2010. Its county seat is Annapolis, which is also the capital of the state. The county is named for Anne Arundell, Lady Baltimore, a member of the ancien…Anne Arundel County, also notated as AA or A.A. County, is a county located in the U.S. state of Maryland. As of the 2020 United States census, its population was 588,261, an increase of just under 10% since 2010. Its county seat is Annapolis, which is also the capital of the state. The county is named for Anne Arundell, Lady Baltimore, a member of the ancient family of Arundells in Cornwall, England, and the wife of Cecilius Calvert, 2nd Baron Baltimore, founder and first lord proprietor of the colony Province of Maryland.