Gregg Township is a township in Union County, Pennsylvania, United States. The population was 4,687 at the 2000 census, of which 3,679 were federal inmates.
Gregg Township, named for U.S. House Representative Andrew Gregg, was founded in 1865, having been carved out of Brady Township, Lycoming County in 1861.
The township shares Union County's rural character, with farms and woodlands dominating. Most of the unincarcerated population lives in the unincorporated hamlet of Allenwood. Just north of the hamlet on U.S. Route 15 is the Allenwood Federal Correctional Complex, with low, medium, and high security federal prisons. With about 4,000 inmates, these facilities contain the great majority of the township's residents.