Geneva Lake was formed some 10,000 years ago as a result of glacial action, which created the lake basin and sculpted the landscape. The geological formation of Geneva Lake begins with the "melt off" of a glacial lobe known as the “Troy Valley.” Troy Valley was a depression running from Troy, Wisconsin through Lyons and then westward through Lake Geneva and toward Beloit. The cascading water from "Troy Valley's" outlet formed connecting channels that evolved into the present lakes Geneva, Delavan and Como.
Geneva Lake took its present shape with the "Late Wisconsin" glacial period when the sedimentary deposits of the "Delavan Lobe" divided Geneva and Delavan, which is three and one half miles to the west. Second sedimentary deposits separated Geneva and Como, which is a mile north of Williams Bay. Both Geneva Lake and Como Lake drain to the east.
The lake was first discovered in 1831 when an Army party, under the command of Major John Kinzie, was traveling along Indian Trails from Fort Dearborn in Chicago to Fort Winnebago near what is today Portage, Wisconsin. The trail led through the Potawatomi Indian Village located on a plateau near the seven ceremonial pools at the western end of the lake. There is a bronze marker located on the south shore lake path just east of Fontana marking the location where the Kinzie party first observed the lake.