According to the United States Census Bureau, the township has a total area of 47.3 square miles (122.4 km2), of which, 47.2 square miles (122.3 km2) of it is land and 0.1 square miles (0.1 km2) of it (0.11%) is water. Rayne township is predominantly rural with several small unincorporated villages.

There were 1,220 households, out of which 33.4% had children under the age of 18 living with them, 69.4% were married couples living together, 5.2% had a female householder with no husband present, and 21.5% were non-families. 19.3% of all households were made up of individuals, and 6.8% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.03.

In the township, the population was spread out, with 23.1% under the age of 18, 7.3% from 18 to 24, 27.5% from 25 to 44, 28.7% from 45 to 64, and 13.4% who were 65 years of age or older. The median age was 41 years. For every 100 females, there were 102.8 males. For every 100 females age 18 and over, there were 101.4 males.

The median income for a household in the township was $37,962, and the median income for a family was $41,250. Males had a median income of $31,548 versus $17,181 for females. The per capita income for the township was $15,806. About 8.0% of families and 10.0% of the population were below the poverty line, including 13.8% of those under age 18 and 12.7% of those age 65 or over.