The Kaiser Family Health Foundation provides lots of information on the state's population including distribution by age, citizenship status, race/ethnicity and information on median incomes, unemployment rate and health status. The site also allows you to compare Wisconsin to the other states in any of these categories.
This U.S. government FedStats site features statistics about the people, businesses and geography of Wisconsin. If students are looking for facts such as state population, percentage population by ethnic groups, average income, land area, etc., this is the place to go.