Illinois State Route 123 runs north-south for aprox. one (1) mile in Sangamon County. IL St Rt 123 does not pass through any towns in Western Sangamon County. IL St Rt 123 is not multi-plexed in Sanamon County. IL St Rt 123 intersects the following highway in Sangamon County. Illinois State Route 125, near Pleasant Plains.
WB IL St Rt 123 at the Sangamon/Menard County Line.
WB IL St Rt 123 at the Menard/Sanagmon County Line.
Sangamon County mile marker at the Menard/Sangamon County Line.