[1] The watershed of the stream has an area of 12.4 square miles (32 km2), making it one of the largest tributaries of the Lackwanna River.

Fall Brook begins in a wetland near Birchtown in Clifford Township, Susquehanna County.

It flows south-southwest for a few tenths of a mile before crossing Pennsylvania Route 247 and turning south.

The stream then turns south-southwest again for several tenths of a mile, receiving an unnamed tributary from the right and exiting Clifford Township and Susquehanna County.

It continues south-southwest for more than a mile, passing through another wetland and receiving several more unnamed tributaries: three from the left and one from the right.

The stream then turns east-southeast, entering a water gap and passing through Fall Brook Lake.

[1] Fall Brook joins the Lackawanna River 28.30 miles (45.54 km) upriver of its mouth.

[6] At its mouth, the peak annual discharge of Fall Brook has a 10 percent chance of reaching 1,210 cubic feet (34 m3) per second.

However, there are also open fields, dairy farms, residential land, and golf courses in this reach of the watershed.

The Fall Brook Reservoir is located in the middle reaches of the watershed, near Pennsylvania Route 106.

Additionally, the first sawmill in Fell Township was built on Fall Brook in 1824 by George Reynolds.

[14] A prestressed box beam or girders bridge carrying T570B was constructed across Fall Brook in 1956.

A prestressed box beam or girders bridge carrying the same highway across the stream in Fell Township was built in 1959 and repaired in 2007.

[15] Channelization work was done on 1.5 miles (2.4 km) of Fall Brook in Carbondale by the United States Bureau of Mines in 1965.

[6] By the early 2000s, a United States Army Corps of Engineers project had been proposed to alleviate flow loss in the stream.

[16] Wild trout naturally reproduce in the stream from its headwaters downstream to Fall Brook Lake, a distance of approximately 4.33 miles (6.97 km).

[17] However, in a February 1992 field survey, the stream was found to be devoid of finned fish, despite having conditions that could support them.

[3] In the early 2000s, the Lackawanna River Watershed Conservation Plan recommended constructing a greenway and/or connecting trail along Fall Brook.

A greenway along the stream's corridor could link Carbondale to the Merli-Sarnoski Park and possibly the watershed of Tunkhannock Creek.

[3] In 2015, the trout fishing season for Fall Brook in Susquehanna County opened on April 18.