According to the United States Census Bureau, the township has a total area of 39.9 mi². 39.7 mi² is land and 0.2 mi² of it is water. The east quarter of the city of Scanlon and the north three-quarters of the city of Thomson are located within Thomson Township geographically but are separate entities. The Saint Louis River flows through at the western edge of Thomson Township. The Midway River and Crystal Creek both flow through Thomson Township.
The township contains three cemeteries, Finnish Apostolic, Saint Matthew's and Thomson, which are all still in use today and one cemetery that is no longer platted, the Pioneer Cemetery at Jay Cooke State Park.
Demographics
As of the census of 2000, there were 4,361 people, 1,527 households, and 1,244 families residing in the township. The population density was 110.0 people per square mile. There were 1,555 housing units at an average density of 39.2/sq mi. The racial makeup of the township was 97.89% White, 0.21% African American, 0.62% Native American, 0.60% Asian, 0.02% from other races, and 0.66% from two or more races. Hispanic or Latino of any race were 0.41% of the population. 26.0% were of Finnish, 13.5% Norwegian, 11.1% Swedish and 6.5% Irish ancestry. There were 1,527 households out of which 41.5% had children under the age of 18 living with them, 73.4% were married couplesliving together, 5.6% had a female householder with no husband present, and 18.5% were non-families. 15.1% of all households were made up of individuals and 5.6% had someone living alone who was 65 years of age or older. The average household size was 2.85 and the average family size was 3.18. In the township the population was spread out with 29.3% under the age of 18, 6.2% from 18 to 24, 29.6% from 25 to 44, 25.6% from 45 to 64, and 9.3% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 101.5 males. For every 100 females age 18 and over, there were 101.5 males. The median income for a household in the township was $53,026, and the median income for a family was $58,977. Males had a median income of $44,547 versus $25,270 for females. The per capita income for the township was $20,045. About 3.2% of families and 5.4% of the population were below the poverty line, including 7.4% of those under age 18 and 4.4% of those age 65 or over.
