McHenry County is under a flood watch until 3 p.m. Thursday, according to the National Weather Service.
About an inch of rain fell overnight on top of frozen ground in north central Illinois, according to the service. This has led to minor flooding throughout the area.
A flood warning from the service said the Fox River at the Algonquin dam may experience flooding.
At 9:30 a.m. Wednesday, the water was at 8.4 feet. Flood stage is at 9.5 feet, according to the service. The river is expected to rise above flood stage by Saturday morning.
If drivers encounter a flooded road, they should turn around and find another route, the service advises.