 Sinnott Township was organized in 1883, and named for J. P. and P. J. Sinnott, early settlers.According to the United States Census Bureau, the township has a total area of 36.2 square miles (93.7 km²), all of it land.As of the census of 2000, there were 52 people, 25 households, and 16 families residing in the township.