Patuxent River

The Patuxent River is a tributary of the Chesapeake Bay in the state of Maryland. Its source is located in the hills of the Maryland Piedmont near the intersection of four counties, Howard County, Maryland, Frederick County, Maryland, Montgomery County, Maryland and Carroll County, Maryland. Flowing in a generally southward direction, the Patuxent crosses the heavily urbanized corridor between Baltimore and Washington, D.C and opens up into a navigable estuary near the town of Deep Landing in Calvert County, Maryland, finding the Chesapeake Bay about thirty miles later.

The river marks the boundary between the counties containing suburbs of Washington, D.C. and those containing suburbs of Baltimore.