Smithville Ditch is a long second-order tributary to Tommy Wright Branch in Caroline County, Maryland. This is the only stream of this name in the United States.
Smithville Ditch rises about southeast of Denton, Maryland, and then flows generally south to join Tommy Wright Branch about west-southwest of Smithville, Maryland.
Smithville Ditch drains of area, receives about 44.6 in/year of precipitation, and is about 12.11% forested.