Between AD 650 and 1200, groups of Native Americans throughout the southern half of Wisconsin and portions of adjacent states built earthen mounds of various shapes and sizes, including mounds shaped like animals, today called effigy mounds. The 11 mounds preserved here in the Jefferson County Indian Mounds and Trail Park were part of a larger group of 78 mounds and include symmetrical and animal shapes, resembling birds, turtles or lizards, and perhaps spiritual figures. A remnant of an ancient trail is also visible in the park.

The people who built effigy mounds hunted and collected food, often returning to the same locations seasonally. They lived in semi-permanent villages, used the bow and arrow, and made and used pottery. Mounds likely served ceremonial, spiritual and practical purposes, perhaps marking territories and designating special gathering places. Mounds often, but not always, contain burials. The Lake Koshkonong area once had 23 effigy mound groups, composed of about 500 individual mounds.