The Allenwood River Bridge and Benjamin Griffey House are listed on the National Register of Historic Places.

[3] The township shares Union County's rural character, with farms and woodlands predominating.

Gregg Township is bordered by Lycoming County to the west and north, the West Branch Susquehanna River to the east, over which lies Northumberland County and White Deer Township to the south.

Gregg Township is the entire portion of Union County lying within the White Deer Hole Valley.

The creek flows east through the township from Lycoming County to its mouth in Allenwood.

20.3% of all households were made up of individuals, and 8.7% had someone living alone who was 65 years of age or older.

This was the subject of a zoning battle in the early 1990s when a Texas waste company called USPCI attempted to locate a toxic waste incinerator across Route 15 from the Allenwood Penitentiary, leading to the local community to unite under the banner of the Organizations United for the Environment.