Sawmill Branch is a long 2nd order tributary to Smyrna River in New Castle County, Delaware.
According to the Geographic Names Information System, it has also been known historically as:
Sawmill Branch rises in a pond on the Blackbird Creek divide about 1.5 miles southeast of Blackbird in New Castle County, Delaware. Sawmill Branch then flows southeast to meet the Smyrna River about 1.5 miles southeast of Chambersville, Delaware.
Sawmill Branch drains of area, receives about 44.0 in/year of precipitation, has a topographic wetness index of 589.76 and is about 18.8% forested.