Garnes Township was named for the phonetic version of the last name of Ellef K. Gjernes,[3] a Norwegian settler[4] from Ål in Hallingdal, Norway, who was the township's first postmaster in 1897.

[5] According to the United States Census Bureau, the township has a total area of 48.3 square miles (125 km2), all land.

There were 80 housing units at an average density of 1.7 per square mile (0.66/km2).

25.7% of all households were made up of individuals, and 11.4% had someone living alone who was 65 years of age or older.

About 8.8% of families and 11.2% of the population were below the poverty line, including 14.0% of those under the age of eighteen and 50.0% of those 65 or over.