Hawlings River is a 12.9 miles (20.8 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Patuxent River

Patuxent River

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...

 in Montgomery County

Montgomery County, Maryland

Montgomery County is a county in the U.S. state of Maryland, situated just to the north of Washington, D.C., and southwest of the city of Baltimore. It is one of the most affluent counties in the United States, and has the highest percentage of residents over 25 years of age who hold post-graduate...

, Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

. The watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 covers an area of about 28 square miles (72.5 km²). The headwaters of the river originate in the area north of Laytonsville

Laytonsville, Maryland

Laytonsville is a town in Montgomery County, Maryland, United States. The population was 277 at the 2000 census. Laytonsville was originally known as Cracklintown. This name originated from the popular cracklin bread, which was baked in the locale. This recipe, essentially a bacon corn bread, also...

, and the river flows southeast, entering the Patuxent about 1.5 miles (2.4 km) below the Triadelphia Reservoir

Triadelphia Reservoir

Triadelphia Reservoir, sometimes called Tridelphia Reservoir or Tridelphia Lake, is located on the Patuxent River, in Howard County and Montgomery County, Maryland near the town of Brookeville. The reservoir was created in 1943 by the construction of the Brighton Dam on the Patuxent. It has a...

. Portions of Hawlings River flow through
Rachel Carson Conservation Park and Hawlings River Stream Valley Park. Tributaries of the Hawlings River include Mount Zion Tributary, Reddy Branch, Olney Mill Tributary, Gregg Tributary, and James Creek. The river and its tributaries total about 98 miles (157.7 km) of streams.