According to the 2023 USDA Hardiness Zone Map Lee County, Illinois is in Zones 5a (-20°F to -15°F) and 5b (-15°F to -10°F). There is no change from the 2012 USDA Hardiness Zone Map which has Lee County in also in Zones 5a (-20°F to -15°F) and 5b (-15°F to -10°F).