U.S. Route 166 (US 166) is a 164-mile (264 km) east–west United States highway. This route and US 266 are the only two remaining spurs of historic U.S. Route 66 (which was decommissioned in 1985), since US 666 was renumbered to US 491 in 2003. US 166 meets the old route of US 66, now designated US 69 Alternate, in Baxter Springs in the southeast corner of Kansas.