It happened in the 40800-block of North Delaney Road in Wadsworth at about 9:10 p.m.
The sheriff's office said a large vehicle, likely a pickup truck, hit the horse while driving north and kept going.
It's unclear if anyone was riding the horse, or if the horse escaped from a nearby ranch.
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The horse had to be euthanized due to the severity of its injuries.
Anyone with information about the horse or the crash should call the Lake County, Illinois Sheriff's Office at 847-377-4000.