Route 66 joined US 40, traversing East St. Louis and Fairmont City. Shortly after Fairmont City, Route 66 passed Cahokia Mounds, later a UNESCO World Heritage Site. It joined IL 157 on the western end of Collinsville, later navigating to modern day I-55 via IL 159. This stretch of Route 66 met the main route in Hamel. Poplar Street Bridge was opened in 1967 to facilitate I-55, I-64, and I-70. US 66 and US 40 were both simultaneously rerouted over this newer bridge instead of the Veterans' Memorial Bridge. Hamel to Springfield Original route U.S. Route 66 originally followed IL 4 north of Hamel. This alignment navigated through Staunton, Sawyerville, Benld, Gillespie and Carlinville to Nilwood. The section of US 66/IL 4 from Nilwood to Girard was listed on the National Register of Historic Places on May 23, 2002. Route 66 continues along IL 4 north through Virden, Thayer, to Auburn. A section of IL 4 north of Auburn and south of Springfield, which was also part of the original span of US 66, was listed on the National Register of Historic Places on August 6, 1998. This is the last brick alignment in Illinois. Route 66 then passed through Chatham, and entered Springfield. Breaking off of IL 4, the route passed the Illinois State Capitol and the Old State Capitol. Eastern alternate route An alternate route northward from Hamel was opened in 1930. It followed IL 4 for , then branched off to the east, bypassing Staunton. The road moved northeast through Mount Olive past the Soulsby Service Station. The alignment from Litchfield to Mount Olive was added to the National Register of Historic Places on November 29, 2001. This segment is a stretch that begins northwest of Mount Olive in southeastern Macoupin County and ends about north of the intersection of US 66 and IL 16 in Litchfield. This alignment passed through North Litchfield, South Litchfield, Cahokia and Mount Olive townships. The terrain through the area is mostly flat. Unlike other sections of Route 66 in Illinois that are listed on the National Register, the segment from Litchfield to Mount Olive does not include any contributing structures such as bridges or culverts. The Ariston Café in Litchfield is the longest-operating restaurant along the former US 66. The Belvidere Café, Motel, and Gas Station also provided services to travelers. This alternate alignment continued north past Waggoner, Farmersville, Divernon, Glenarm