Illinois Route 164 runs east-west in Henderson and Warren County, skirting north and south of US Route 34. It starts at US Route 34 on the east side of the Mississippi River from Burlington, Iowa, running north to Oquawka. At Oquawka, the county seat of Henderson County, Illinois 164 turns into the easterly alignment that comprises most of its length. Illinois 164 connects rural areas with Monmouth, then continues east as somewhat of an alternate to US Route 34 until it ends at Galesburg.
Illinois 164 begins at US Route 34 just east of Burlington, Iowa. It heads north through Gladstone.
Illinois 164 turns easterly in Oquawka.
Illinois 164 crosses Illinois 94 about five miles east of Oquawka:
Illinois 164 meets Illinois 135 at the southern end of that route:
Illinois 164 reaches US Route 34 and US Route 67 on the west side of Monmouth, and joins these two routes north.
Wrapping around on the north side of Monmouth, US Route 67 splits to the north, leaving Illinois 164 with US Route 34 eastbound...
Illinois 164 splits off of US Route 34 to head away from Monmouth. For the remainder of Illinois 164's length, the state route serves as a northern alternate to the four-laned US Route 34...
Finally, Illinois 164 ends at yet another encounter with US Route 34, but this time, it's in Galesburg at a point common to the north end of Illinois 41.