This dataset represents boundaries for unified school districts within the state of Wisconsin in 2021. By law, all territory in the state must be included within a public school district. The US Census Bureau identifies three types of school districts. Unified school districts serve children of all grade levels, Elementary primarily serve students in the elementary grades, and Secondary primarily serve children in grades 9-12. Out of 421 school districts in Wisconsin, 368 are considered unified districts. This layer is an aggregate of county-submitted data for school district boundaries based on 2019 tax parcel data. Boundaries for this layer may vary greatly in areas compared to the 2017, 2018, and 2019 layers. Please refer to the Lineage section for more information on these boundary changes.Each year, there is a chance for reorganizations to take place that either transfer territory between school districts or consolidate/dissolve/create districts. These reorganizations go into effect on July 1st of each year. In 2020, there were six (6) reorganizations that involved unified school districts. The reorganizations took place in Dane, St. Croix, and Waukesha counties. Transfers of territory took place between the following pairs of districts: Mineral Point and Iowa-Grant; Norris and Mukwonago; Middleton-Cross Plains and Madison Metropolitan; New Richmond and Somerset; and Middleton-Cross Plains and Wisconsin Heights. Please refer to the property transfer log for more information.This is not an official authoritative statewide dataset for unified school district boundaries nor does one exist for Wisconsin. The boundaries reflect tax parcel data submitted by Wisconsin counties in January of each year. These boundaries are updated annually around July 1 to reflect boundary changes from the reorganization process and as needed throughout the rest of the year.