1637 - St. Mary's created as original colony. Covered both sides of Chesapeake Bay.

1642 - Kent created from St. Mary's east of the bay.

1650 - Anne Arundel and Charles Counties are created from St. Mary's.

1654 - Patuxent is created from St. Mary's; Charles (old), non-county area. Charles (old) abolished. Anne Arundel name changed to Providence. St. Mary's name changed to Potomac.

1658 - Charles is created from Potomac. Patuxent name changed to Calvert. Potomac name changed back to St. Mary's. Providence name changed back to Anne Arundel.

1659 - Baltimore is created from Anne Arundel, Kent and non-county area.

1662 - Talbot is taken from Kent.

1666 - Somerset is taken from non-county area and extends to Atlantic.

1669 - Dorchester is created from non-county area; Durham and an unnamed county are created from Somerset in an area that is now Delaware.

1671 - Kent gained from Talbot but still appears smallest of counties.

1672 - Worcester is created from Durham and the unnamed county in the area that is now Delaware.

1674 - Cecil County is created from Baltimore.

1685 - There was a royal decision dividing peninsula between Maryland and Delaware Colony but the boundary was not established. Worcester County, Md., was effectively eliminated.

1695 - Prince George's was created from Charles, Calvert and non-county area effective 1696.

1696 - Prince George's organized. Charles and St. Mary's gained from Calvert. Kent exchanged land with Talbot.

1698 - Anne Arundel exchanged land with Baltimore.

1706 - Queen Anne's was created from Kent, Talbot and Dorchester, effective 1707.

1707 - Kent gained from Cecil (but lost to Queen Anne's).

1727 - Anne Arundel gained from Baltimore.

1742 - Worcester was created from Somerset 1748 - Frederick was created from Prince George's and non-county area. Charles gained from Prince George's on the Potomac.

1750 - Frederick gained from Baltimore.

1773 - Harford was created from Baltimore effective 1774 and Caroline was created from Dorchester and Queen Anne's effective 1774.

1776 - Montgomery and Washington were created from Frederick.