WI Sec of State Hosts Digital Archive of Municipal Records
The Wisconsin Office of the Secretary of State maintains a digital archive of state municipal records - some more than 100 years old.
Records from Wisconsin's towns, villages, cities and counties include incorporation papers, charters, annexations, corporate boundaries, maps and litigation correspondence.
For example, see this 1921 map of the Original City of Madison with Subsequent Annexations.
Source: Found in Wisconsin