The National Weather Service in Paducah says a Heat Advisory has been extended and now remains in effect until 8pm Thursday for portions of Southern Illinois.
Maximum heat index values could reach near 110 degrees, with the combination of hot temperatures and high humidity increasing the risk of heat-related illnesses.
Forecasters say the heat will not disappear quickly, with daily heat index values expected to remain near or above 100 degrees through next weekend.
Residents are encouraged to drink plenty of fluids, stay in air-conditioned areas when possible, avoid prolonged exposure to the sun and check on relatives, neighbors and pets.