[1] The Goose Lake region formed in the post-Wisconsin glaciation period as a flat, wet area dominated by layers of sand and silt laid down by postglacial outwash.

While the flat, alluvial soil of this riparian bottomland was intensely fertile, the lack of adequate drainage made the land of the Goose Lake country unsuitable for subdivision for agriculture.

Some of them were trained potters; they fired the clay in kilns to create pieces of earthenware for frontier farm and household needs.

The area's defining geographical feature disappeared and was replaced by damp farmland and wet pastureland.

Today, the park's Marsh Loop Trail passes over part of the bed of the vanished lake.

Unlike many of Illinois's state parks, Goose Lake Prairie is not primarily managed for hunting; visitors are encouraged to enjoy a tallgrass prairie ecosystem, dominated by grasses such as big bluestem, Indian grass, and switchgrass, and by flowering forbs such as compass plants, coneflowers, goldenrod, shooting stars, and violets.

The patches of old-growth tallgrass prairie that have survived to the present day serve as a biotic refuge for many species that can live nowhere else, especially prairie-endemic moths and butterflies.

Lepidopterists have found the papaipema moth, previously thought to be extinct, fluttering about Goose Lake Prairie's forbs and flowers.