Interstate 90

Interstate 90 enters the state of Wyoming from the north, following U.S. 87 en route from Billings and Hardin toward Sheridan. The freeway follows the foothills of the Bighorn Mountains between Sheridan and Buffalo, then turns east across the Powder River Basin toward Gillette, Moorcroft, and Sundance. Interstate 90 shares alignments with both U.S. 14 and U.S. 16 along this path. Upon entering the Wyoming Black Hills, Interstate 90 sees rolling, forested hills amid the plains. Interstate 90 leaves Wyoming and enters South Dakota between Sundance and Spearfiesh; the freeway then proceeds southeast toward Rapid City. Nationally, Interstate 90 is a transcontinental freeway that extends from Washington 519 and the Seattle King Dome (demolished in 2000) just west of Interstate 5 in Seattle, Washington, east to Logan International Airport in Boston, Massachusetts (via a new tunnel link to the airport from the current end of Interstate 90 at Interstate 93 as part of the "Big Dig" project). For more detail on I-90 nationwide, please visit Interstate 90 at Interstate-Guide.

Major Cities

Nationally, Interstate 90 serves the following cities/points of interest: Seattle, Spokane, Coeur d'Alene, Missoula, Butte, Bozeman, Billings, Sheridan, Buffalo, Gillette, Sundance, Spearfish, Rapid City, Wall, Chamberlain, Mitchell, Sioux Falls, Worthington, Albert Lea, Austin, Rochester, La Crosse, Tomah, Madison, Rockford, Chicago, Gary, South Bend, Toledo, Cleveland, Erie, Buffalo, Rochester, Syracuse, Utica, Schenectady, Albany, Troy, Pittsfield, Springfield, Worchester, and Boston.

Interstate 90 Wyoming Guides


Interstate 90 replaces or parallels U.S. 87 between the Montana State Line and the Interstate 25 interchange in Buffalo. Shared alignments are well-signed for both Interstate 90 and U.S. 87. At Buffalo, U.S. 87 and Interstate 25 proceed south toward Casper, while Interstate 90 turns east toward Gillette and Rapid City. The freeway roughly parallels both U.S. 14 and U.S. 16 along the best and most direct route between Buffalo and Rapid City. U.S. 14 and U.S. 16 share alignment with Interstate 90 or take looping routes away from the freeway to connect to scenic areas or nearby cities and points of interest not on Interstate 90.

Interstate 90 was the last Interstate highway to be completed in the state of Wyoming. The last segment of was the ten-mile stretch from the Montana State Line to Ranchester in Sheridan County. The construction of this route, completed on July 8, 1985, corresponded with the opening of the adjoining 22-mile section of Interstate 90 in Montana. With this construction, Wyoming became one of the first states to complete its portion of the Interstate Highway System. The following chart provides the opening month and year for each segment of Interstate 90 in Wyoming:

Section Length Month Opened
Montana State Line to Ranchester (U.S. 14) Interchange 10.1 10/85
Ranchester (U.S. 14) Interchange to Monarch 5.4 11/83
Monarch to North Sheridan (Business Loop I-90) Interchange 6.9 9/61
Sheridan Marginal 4.45 7/62
South Sheridan (Business Loop I-90, U.S. 14) Interchange to Piney Creek Interchange (Johnson County) 19.9 12/68
Piney Creek Interchange to Lake De Smet Interchange 7 11/65
Lake De Smet Interchange to North Buffalo (Business Loop 90) Interchange 4.2 10/63
North Buffalo (Business Loop I-90) Interchange to Interstate 25 Trilevel Interchange 2.4 10/64
Interstate 25 Trilevel Interchange to Gillette (Campbell County); the section of Interstate 90 between the Crazy Woman Interchange and Dead Horse Creek was only two lanes wide until 10/69 65.1 10/62
West Gillette (Business Loop I-90) Interchange 0.4 8/70
Gillette Marginal: West Gillette (Business Loop 90) to Garner Lake Road 3.8 9/73
Garner Lake Road to four miles east of Rozet 7.4 11/76
Four miles east of Rozet to Jeffers Road 9.7 10/76
Jeffers Road to West Moorcroft (Business Loop I-90) Interchange (Crook County) 7.8 8/72
Moorcroft Marginal 1.9 4/67
East Moorcroft Interchange (Business Loop I-90) Interchange to West Sundance (Business Loop 90) Interchange 30.7 10/63
Sundance Marginal 4.1 2/73
West Sundance (Business Loop I-90) Interchange to five miles east of Sundance 5.3 10/76
Five miles east of Sundance to two miles east of Aladdin 6.6 6/78
Two miles east of Aladdin to South Dakota State Line 5.65 10/78


Interstate 90 enters Wyoming together with U.S. 87 from the northern tier state of Montana. U.S. 87 is one of the more ubiquitous U.S. routes in Wyoming, having been routed at one time or another in some of the most populous areas of the state. This highway once defined Wyoming, but today it is mired in the shadow of the Interstates: Interstate 90 from the Montana State Line to Buffalo and Interstate 25 from Buffalo south to Raton, New Mexico.

Nationally, Interstate 90 is the longest Interstate highway by mileage, and it has become longer. Separate projects resulted in Interstate 90 gaining ground at both of its ends. Interstate 90 was extended in the late 1980s to connect to Interstate 5 in Seattle, and the Big Dig project in Boston resulted in Interstate 90 (Massachusetts Turnpike) extending to the entrance of Logan International Airport (to end at Massachusetts 1A) via a series of tubes under Boston Harbor. This extension was completed in 2003.

Along Interstate 90 in Sheridan and Johnson Counties lies a terrific history of the frontier. The Powder River War, the Battle of Tongue River, Connor Battlefield, and Sawyer Battlefield are all along this route. The frontiersmen and the Native Americans battled frequently in the later 1800s, but the frontiersmen ultimately won out. Today, ancestors of the Native Americans are on reservations, while the white man roams freely. These reservations typically were made from what the white man considered less-than-desirable land. The containment of Native Americans on reservations led to some serious decline, both economically and socially. Fortunately, the long-term trend of poverty is changing, but for more on the plight of the Native Americans as well as a history of the frontier, we recommend the 1965 History of Wyoming, which was written by the late Dr. T.A. Larson, a professor emeritus from the University of Wyoming.

Interstate 90 enters Sheridan, the fifth-largest city in the state, just south of the ranching community of Ranchester. Sheridan is the gateway to the Big Horn Mountains, a popular recreation area just west of Sheridan on U.S. 14. Sheridan, founded in 1873 as Mandel and renamed Sheridan in 1882, has the strong base of the energy industry. However, it is not nearly as reliant on energy as Gillette, its rival city further east on Interstate 90. Sheridan has a natural beauty that Gillette simply doesn't possess. But Gillette has more raw material wealth than Sheridan, so it's a trade-off. Townsfolk in Sheridan and Gillette sometimes don't see each other all year until that time of fall when Sheridan High School and Gillette High School take each other on in football. This is a very big rivalry, akin to the two Cheyenne high schools or Rock Springs versus Green River.

Interstate 90 spins off a business loop into downtown Sheridan, which leads to several historic buildings, including the supposedly haunted Sheridan Inn. There are also the usual gamut of motels, museums, and other tourist affects to placate those on their way to Yellowstone. South of Sheridan, U.S. 87 provides a scenic alternate route, as it passes by the Fetterman Monument, the Wagon Box Fight site, and Fort Phil Kearney. A detour is in place via Story because a portion of U.S. 87 was destroyed by a landslide. Interstate 90, meanwhile bypasses the historic sites along U.S. 87, but the two routes rejoin in Johnson County.

U.S. 87 does not remain with Interstate 90 for long. At Buffalo, U.S. 87 turns south toward Casper. Interstate 25 begins its southward journey at Buffalo, heading south with U.S. 87 to Casper, Cheyenne, and points beyond. Buffalo is named after its sister city in Buffalo, New York. Buffalo is a gateway to the Big Horn Mountains to the west (via U.S. 16 and the Powder River Pass) and to the "Energy Capital of the World," Gillette, to the east. Interstate 90 travels through some high desert and sagebrush as it heads east from Buffalo toward the Razor City.

Campbell County, home of Gillette, has been well-known for its huge stockpile of crude oil. But a more recent find of huge quantities of low sulfur coal has made Campbell County and Gillette known as the energy capital of the world. Gillette is rapidly growing due to the energy boom, and some speculate it will be one of the largest cities in the state within ten years. But as is indicative of the boom-and-bust cycle of mining and energy, one can never be too sure.

U.S. 14 and U.S. 16 parallel Interstate 90 along the eastern half of its route, but they split from the route at Moorcroft. U.S. 16 will not rejoin Interstate 90 again until it reaches its terminus in Rapid City (the Interstate 190 exit). U.S. 14 takes a short loop leading to Devil's Tower, then returns to Interstate 90 at Sundance. Either way, Interstate 90 cuts the most direct route (without going through Custer National Forest or Mount Rushmore) to Rapid City.

Interstate 90 hits Sundance a rather short distance after Moorcroft. Sundance is actually a neat little town, with a cool name and lots of scenic beauty, including Sundance Mountain. Look for the pine trees, bluffs, and gorges that mark this part of Wyoming. So did Crook County get its name from all the crooks hiding out in the gorges? No, it got its name from General George Crook, an early frontiersman who was also involved in some skirmishes with the Native American population.

East of Sundance, Interstate 90 passes by some abandoned mining camps (Mineral Hill and Welcome). Much of the remaining area has deserted and deteriorating buildings. By the time you see the signs for Beulah, your already entering South Dakota, the land of famous faces (as seen on Mount Rushmore).

Page Updated June 9, 2012.

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