Somerset County is the southernmost county in the American State of Maryland. As of the 2010 census, the population was 26,470. making it the second-least populous county in Maryland. The county seat is Princess Anne. The county was named for Mary, Lady Somerset, the wife of Sir John Somerset and daughter of Thomas Arundell, 1st Baron Arundell of Wardour (ca 1560-1639). She was also the sister of Anne Calvert, Baroness Baltimore (1615-1649), who later lent her name to Anne Arundel County, which was erected in 1650 as the Province of Maryland's third county.