County County Seat Date Formed Created From Allegany Cumberland 1789 Washington Ann Arundel Annapolis 1650 Original county Baltimore Towson By 1659/60 Original county Baltimore City N/A 1851 Baltimore County Calvert Prince Frederick 1654 Original county Caroline Denton 1773 Dorchester & Queen Anne's Carroll Westminster 1837 Baltimore & Frederick Cecil Elkton 1674 Baltimore & Kent Charles La Plata 1658 Original county Dorchester Cambridge 1669 Somerset & Talbot Frederick Frederick 1748 Baltimore & Prince George's Garrett Oakland 1872 Allegany Harford Bel Air 1773 Baltimore Howard Ellicott City 1851 Anne Arundel Kent Chestertown By 1642 Original county Montgomery Rockville 1776 Frederick Prince George's Upper Marlboro 1696 Calvert & Charles Queen Anne's Centreville 1706 Dorchester, Kent & Talbot St. Mary's Leonardtown 1637 Original county Somerset Princess Anne 1666 Original county Talbot Easton by 1661/62 Original county Washington Hagerstown 1776 Frederick Wicomico Salisbury 1867 Somerset & Worcester Worcester Snow Hill 1742 Somerset