U.S. Route 34 in Colorado is a segment of U.S. Route 34. Its west end is at U.S. Route 40 in Granby and its east end is at the Nebraska border east of Laird, Colorado.

The route begins in Granby at US 40. It then follows the Colorado River Valley near Granby Lake and enters Arapaho National Recreational Area.

After entering Rocky Mountain National Park in Colorado's Front Range[citation needed], US 34 follows the North Fork Colorado River through Kawuneeche Valley. It passes over Milner Pass and reaches the Alpine Visitor Center. Then it continues east, passing its highest point at 12,183 feet near the Gore Range. It exits the park at US 36 at Deer Ridge Junction.

US 34 here is the highest continuous highway in the United States.

This section of US-34 requires a $20 national park entrance fee, making this segment into a toll road.

From here, it passes by Estes Park as Eisenhower Boulevard, has a business route and enters Loveland, becoming a four-lane expressway. Here, it intersects I-25 and U.S. Route 287.

At Greeley, it passes by U.S. Route 85 in a complex interchange and U.S. 34 Business, and crosses the South Platte River. It also has an interchange with SH 257. From here, it is no longer an expressway. It intersects CO 144 and CO 39, then joins I-76 at Wiggins. It leaves, and follows the North Fork Republican River east into Nebraska, where it intersects CO 71, CO 52, CO 63, CO 61, CO 59, and U.S. Route 385.

Parts of the route were originally designated as US 38. US 34 was extended into Colorado in 1939.

U.S. Route 34 Business serves Estes Park, Colorado. Both of its termini are at US 34. The business route splits from the main route east of the Rocky Mountain National Park Fall River Entrance Station, in the western city limits of Estes Park and enters town on West Elkhorn Avenue. The main route continues around the northern edge of Estes park on Wonderview Avenue, passing a large number of motels. At Moraine Avenue, It joins US 36 in downtown Estes Park. It returns to US 34 after about 1.7 miles (2.7 km) at an intersection with Wonderview Avenue, Big Thompson Avenue, and North St. Vrain Avenue. The business route was established in 1964.

The entire route is located in Larimer County.