DeKalb County is in Northern Illinois. Of the 102 counties in the Prairie State, 634-square-mile DeKalb County ranks 31st by size. Browse all DeKalb County ranches for sale on the Land Network to find the ranch that's right for your business or commercial needs, from the sprawling legacy ranch to unbelievable residential ranch for your second home, investment property or retirement nest egg. The most common type of land for sale by combined acreage in DeKalb County is house.