A low of 35 degrees is possible Thursday evening in Decatur, according to the National Weather Service. Frost is possible after 4 a.m.
The cold snap continues into Friday, with a low of 34 degrees, areas of frost before 9 a.m. and showers in the afternoon.
The average date of the first freeze is between Oct. 7 and 14 in the central and southeastern parts of the state, the weather service said.
The first hard freeze, when temperatures hit 28 degrees or colder, typically happens during the last 10 days of the month.
Patchy fog and a low of 52 are expected Saturday.
The Great River Road
Shawnee Hills Wine Trail
Rader Family Farms
Starved Rock State Park
The Morton Arboretum
Lincoln Memorial Garden Nature Center
Chautauqua National Wildlife Refuge
Buffalo Rock State Park
Rock Springs Conservation Area
Weldon Springs State Park
Newton Lake State Fish and Wildlife Area
Hardy's Reindeer Ranch