The redistricting process begins with each decennial census, when the U.S. government provides detailed census tract data to the states, usually by March 1 of the first year of the decade. In Wisconsin, the state then provides the data to the counties, and each of Wisconsin's 72 counties—in collaboration with the counties' municipal governments—draws new county board and municipal ward boundaries. Counties are required to submit draft boundaries within 60 days of receiving the census data, and no later than July 1 of the first year of the decade. Over the 60 days beginning that July 1, counties and municipalities are directed to come to agreement on their final ward plan and update the county district plan to reflect the agreed wards. Collaboration is necessary because, while the county government ultimately controls the county board districts, the municipal ward boundaries are defined by the municipal governments, and the county board must adhere to the ward lines drawn by the municipalities in the formation of county districts. Wisconsin law does not require wards to be equal in population, but does specify a range depending on the size of the municipality:
