The "Delavan lobe" of this glacier broke off, pushing southwest into the area of Walworth County.

The effigy mounds they erected along the shores of Delavan Lake numbered well over 200, according to an archeological survey done in the late 19th century by Beloit College.

In accordance with the Treaty of Paris (1783), it was turned over to the United States and became part of the newly established Northwest Territory.

Its famous rogue elephant, "Romeo", stood 10+1⁄2 feet (3.20 m) high, and 10,500 pounds (4,800 kg).

Over 130 members of Delavan's 19th century circus colony are buried in Spring Grove and St. Andrew cemeteries.

On July 21, 1948, Delavan was the site of Wisconsin's Circus Centennial as part of the state's celebration of 100 years of statehood.

[5] On May 2, 1966, Delavan was selected by the U.S. Post Office to issue on a first day cover basis, the five-cent American Circus commemorative postage stamp.

One of the major manufacturing and industrial centers of Walworth County, Delavan is home to over 230 businesses including such companies as Borg Indak, Pentair, Andes Candies, Waukesha Cherry-Burrell, Ajay Leisure Products and Outboard Marine Corp.[10] City events include the Delavan Train Show in March, Cinco de Mayo in May, and Scarecrow Fest in September.

The Wisconsin and Southern Railroad continues to service Delavan from a connection at Bardwell to the west.