The town of Washington Island is made up of a group of small islands that includes Plum Island, Detroit Island, Hog Island, Rock Island, Pilot Island, Fish Island, and the largest, Washington Island. The majority of the population of the town lives on Washington Island and many of the other smaller islands are partly or entirely State Parks or National Wildlife Refuges, with small population, if any. As a result, the area is rarely if ever referred to as the town of Washington or just Washington; more commonly the names of the individual islands are used as a reference.
Most of the people who settled on Washington Island were Scandinavian immigrants, especially Icelanders. Today, Washington Island is one of the oldest Icelandic communities in the United States and among the largest outside of Iceland itself.
According to the United States Census Bureau, the town has a total area of 125.5 square miles (325.0 km²), of which, 25.5 square miles (66.0 km²) of it is land and 100.0 square miles (259.0 km²) of it (79.69%) is water.
The land area is composed of Plum Island, Detroit Island, Washington Island, Hog Island, Pilot Island, Fish Island, and Rock Island. Washington Island is the largest in a chain of islands extending across Lake Michigan between the Door Peninsula in Wisconsin and the Garden Peninsula in Delta County, Michigan. These islands are outcroppings of the Niagara Escarpment.
The 2010 US Census lists 708 residents.
In the older 2000 census, there were 660 people, 293 households and 198 families residing in the town. The population density was 25.9 people per square mile (10.0/km²). There were 903 housing units at an average density of 35.4 per square mile (13.7/km²). The racial makeup of the town was 98.79% White, 0.30% Asian, and 0.91% from two or more races. Hispanics or Latinos of any race were 0.15% of the population. 24.9% were of German, 15.3% Norwegian, 12.3% English, 9.1% Danish, 8.8% Irish and 6.1% Icelandic ancestry according to Census 2000.
There were 293 households out of which 25.3% had children under the age of 18 living with them, 59.0% were married couples living together, 6.1% had a female householder with no husband present, and 32.1% were non-families. 30.4% of all households were made up of individuals and 17.1% had someone living alone who was 65 years of age or older. The average household size was 2.25 and the average family size was 2.79.