The Patuxent River is a tributary of the Chesapeake Bay in the state of Maryland. There are three main river drainages for central Maryland: the Potomac River to the west passing through Washington, D.C., the Patapsco River to the northeast passing through Baltimore, and the Patuxent River between the two. https://en.wikipedia.org/wiki/Patuxent_River

It is the largest and longest river entirely within Maryland, and its watershed is the largest completely within the state.