| State: | CO |
| Type: | US |
| Route: | 6 |
| Map Custom: | yes |
| Map Notes: | US 6 highlighted in red |
| Length Mi: | 467.284 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | at the Utah state line |
| Junction: |
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| Direction B: | East |
| Terminus B: | at the Nebraska state line |
| Counties: | Mesa, Garfield, Eagle, Summit, Clear Creek, Jefferson, Denver, Adams, Weld, Morgan, Washington, Logan, Phillips |
| Previous Type: | SH |
| Previous Route: | 5 |
| Next Type: | SH |
| Next Route: | 7 |
| Alternate Name: | Grand Army of the Republic Highway |
U.S. Highway 6 (US 6) is a part of the United States Numbered Highway System that travels from Bishop, California, to Provincetown, Massachusetts. In the U.S. state of Colorado, US 6 is an east–west highway stretching from Utah to Nebraska. Much of the route overlaps other highways in Colorado, and, as a result, much of US 6 is unsigned.
US 6 is concurrent with Interstate 70 (I-70) for a significant portion of its length from the Utah state line to Denver. When the highway enters the western Denver suburbs, US 6 coincidentally aligns with 6th Avenue in the grid system, where it is known as 6th Avenue Freeway. Once it reaches I-25, US 6 travels north briefly, then follows I-76 for most of its length east of Denver. It is unsigned while it is overlapped. The highest altitude along US 6 is 11990feet at Loveland Pass, where it crosses the Continental Divide. It continues down the Clear Creek valley until it reaches I-70, where it is briefly overlapped until I-70 leaves the Clear Creek valley. US 6 continues down Clear Creek and into Denver, where it turns into a freeway with six lanes. East of Denver, it continues east while joined with I-76 until it reaches Sterling, where it diverges from the Interstate. The last town in Colorado through which it passes is Holyoke.