Mill Creek rises in Montgomery County, Pennsylvania; runs southeasterly to West Philadelphia, where it enters 19th-century sewer pipes; and debouches roughly five miles later in the Schuylkill River near The Woodlands Cemetery.

It starts near Narberth, where its source is buried, then runs free for a mile or so before entering Philadelphia at the Overbrook station.

[4] As urban development began in West Philadelphia, the city covered several stream beds with cisterns and a layer of fill deep enough to level the land so that it could be platted into a regular street grid.

The covering of Mill Creek began in 1869, encapsulating the watercourse in a 20-foot (6.1 m)-diameter drainpipe said to be the largest sewer pipe in the world at the time.

[6] Its burial was completed around 1895, allowing the grid of rowhouse development to continue toward the city's western edge at Cobbs Creek.