Nancy Run begins near the Green Pond Golf Course in Bethlehem Township, Pennsylvania.

The creek then receives an unnamed tributary from the left and turns west for some distance before entering the census-designated place of Middletown.

[2] At its mouth, the peak annual discharge of Nancy Run has a 10 percent chance of reaching 3,605 cubic feet per second (102.1 m3/s).

[5] Above its unnamed tributary, the peak annual discharge of Nancy Run has a 10 percent chance of reaching 1,022 cubic feet per second (28.9 m3/s).

[5] Nancy Run was entered into the Geographic Names Information System on August 30, 1990 due to its presence on a 1975 county highway map published by the Pennsylvania Department of Transportation.

[12] Wild trout naturally reproduce in Nancy Run from its headwaters downstream to its mouth.

[15] In the 1990s, Nancy Run was found to support a benthic ecosystem of high biodiversity, including one sensitive species.

[16] Macroinvertebrate taxa found in Nancy Run in the 1970s include Oligochaeta, sowbugs, scuds, mayflies, caddisflies, beetles, Diptera (flies/midges), blackflies, and snails.