Colorado State Highway 128
|Maintained by CDOT|
|Length:||10.0 mia[›] (16.1 km)|
|West end:||SH 93 south of Boulder|
| SH 121 in Broomfield
US 287 in Broomfield
|East end:||I‑25 in Westminster|
|Counties:||Boulder, Broomfield, Adams|
The route begins in the west at a junction with State Highway 93 roughly thirteen miles south of Boulder. From there, the road proceeds eastward into the northern portions of the Denver metropolitan area. The road passes through portions of the cities of Superior, Broomfield, Northglenn, and Westminster and crosses State Highway 121 before being split by a 3.8 mi (6.1 km) section of concurrency with U.S. Route 287 and again resuming its course towards its eastern terminus at exit 223 of Interstate 25 in the city limits of Westminster.
The route was established in the early 1920s, when it began at Federal Boulevard and ended at SH 185 (now deleted). A section from U.S. Route 85 to U.S. Route 6 was added by 1939 and deleted by 1949. The west terminus was extended from U.S. Route 36 to Indiana Street in 1965 and to its current terminus at State Highway 93 two years later.
|Boulder||0.000||0.000||SH 93 – Arvada, Boulder||Western terminus|
|City and County of Broomfield||7.973||12.831||SH 121 (Wadsworth Parkway) to US 36 / US 287|
|Gap in route|
|12.168||19.582||US 287 (Federal Boulevard)|
|Adams||Thornton||14.113||22.713||I‑25||Northern terminus; exit 223 on I-25|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi
^ a: The 3.8 mi (6.1 km) long section of concurrency with US 287 is not maintained with state funds and therefore not considered to be part of SH 128 by the Colorado Department of Transportation. There is also a brief gap of much less than a mile between the junction of SH 128 and SH 121 and the junction of SH 121 and US 287 that is not even nominally part of SH 128. With these sections included, the total end-to-end length is almost exactly 14 mi (22.5 km).