The Town of Plymouth is situated on the southwest quarter of Rock County, bordered on the north by the Town of Center, east by the Town of Rock, south by the Town of Newark, and west by the Town of Spring Valley.  It is southwest of the City of Janesville and northwest of the City of Beloit.  The Villages of Footville and Orfordville border the Town of Plymouth.  According to the United States Census Bureau, the town has a total area of 35.7 square miles (92.3 km²), of which, 35.6 square miles (92.3 km²) of it is land and 0.03% is water.

The Town Hall is located south of Highway 11 West, just off  County Road H on High St.  in unincorporated Hanover.  It is the polling place for all elections as well as the location for all Town meetings.

However if a specific notice is required to be posted in three places, it will be posted in addition to the Plymouth Town Hall and the Town's website at the American Legion in Orfordville and the Sanitary District's Office north of Hanover.  If a notice is required to be published in a newspaper, the Brodhead Independent Register is used.