Illinois Under Ice: The Glaciers That Shaped the Prairie State

Yes. During the Pleistocene Epoch (Ice Age), massive continental glaciers covered nearly all of Illinois multiple times.

Key Glacial Episodes

• Pre-Illinoian (>190k ya): Earliest advances, evidence mostly buried.
• Illinoian (~190–130k ya): Covered ~90% of state; southern limit near Carbondale.
• Wisconsinan (~75–12k ya): Last major advance; covered northern & central IL; reached max ~20k ya (Last Glacial Maximum).

Legacy Landscape

As the Wisconsin Glacier retreated (~14–12k ya), it left:

• Moraines: Ridges of debris (e.g., Bloomington, Urbana, Park Ridge).
• Outwash Plains: Flat, sandy deposits from meltwater (central IL farmland).
• Kettle Lakes: Depressions from buried ice blocks (Chain O'Lakes, many northern lakes).
• Driftless Area (NW corner): Unglaciated—rugged, karst topography (Galena, Apple River Canyon).
• Rich Soils: Glacial till + loess = world-class Mollisols (prairie soils).

Chicago sits on glacial Lake Chicago beach ridges; the "hills" are ancient shorelines.