Potomac River, for a short distance.
The Potomac River divides Maryland and Virginia (The Southern Border) , but Virginia does not own half of the Potomac River.
The Potomac River forms most of Maryland's western boundary.
The Mason-Dixon Line. Surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute between British colonies in Colonial America. It forms a demarcation line between four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and West Virginia (then part of Virginia).
The Potomac River separates Maryland and Virginia.
The Mississippi river forms the boundary between Missouri and Illinois!
The Ohio River forms the western boundary of West Virginia.
The Atlantic Ocean forms the state's eastern boundary.
The Atlantic Ocean.
What saint Lawrence river forms a boundary between the Canadian province of
The Ohio River forms the boundary between Indiana and Kentucky.
The Mason Dixon line forms part of the southern boundary of the state of Pennsylvania. It also forms the northern and eastern boundries of Maryland and a part of the northern boundry of West Virginia, then Virginia and the western border of Delaware. The line was surveyed in the 1760's by Mason and Dixon to settle some land disputes.
The Ohio River forms the boundary between Indiana and Kentucky.