High Quality Content by WIKIPEDIA articles! In the U.S. state of Illinois, Interstate 94 generally runs north–south through the northeastern portion of the state, in Lake and Cook Counties. It is marked east–west in Illinois in accordance with its general alignment across the country, although some entrances on the Tri-State Tollway have north or south I-94 signs. I-94 in Illinois is 78.00 miles (125.53 km) long.