 Vermilion County, out of which Iroquois County was originally formed, lies to the south.To the west is Ford County.The Iroquois River enters the county from Indiana and flows westward along the south side of the village of Iroquois, then along the north side of the city of Watseka, whereupon it veers to the north and joins the larger Kankakee River near the city of Kankakee in the county of the same name; the Kankakee River then flows into the Illinois River further to the northwest in Will County.