[3] The township is in southwestern Greene County and is bordered to the south by the state of West Virginia.

According to the United States Census Bureau, the township has a total area of 23.1 square miles (59.7 km2), all land.

[3] The township is drained primarily by Dunkard Creek, an eastward-flowing tributary of the Monongahela River.

Unincorporated communities in Gilmore Township include Ashtree, Triumph, Sandrock, Hero, Jollytown, and Pine Bank.

28.1% of all households were made up of individuals, and 14.0% had someone living alone who was 65 years of age or older.