U.S. Route 191 (US 191) is a north–south U.S. Highway in eastern Arizona. The highway runs for , making it Arizona's longest numbered highway. The highway begins at State Route 80 near Douglas and crosses over the Utah state line near Mexican Water in the Navajo Nation. Between Douglas and Utah, US 191 shares multiple concurrencies with I-10, US 70, US 180, US 60, SR 61, I-40, SR 264, and US 160.

Until 1981, the route taken by US 191 between I-40 in Chambers and the Utah state line was designated as SR 63. The route from SR 80 in Douglas to I-40 in Sanders was originally designated as part of US 666. US 666 was often associated with the biblical devil, due to the number 666 occasionally being considered the "number of the beast." The highway number caused discomfort with the general public and led to the constant sign theft of US 666 markers along the highway, prompting the redesignation of US 666 as a section of US 191 in 1992.

Route description With a total length of , the section of U.S. Route 191 (US 191) through Arizona has the longest distance of any numbered highway within the state. US 191 almost traverses the entire length of Arizona, but just short of the Mexican border at SR 80 near Douglas. However, the route is connected to the border via SR 80 and US 191 Business (which has no direct connection to US 191 proper). Large sections of the serpentine route taken by US 191 are indirect and include switchbacks in the mountainous regions near Alpine. Part of US 191 is designated as the Coronado Trail Scenic Byway, between Clifton and Springerville.

Douglas to Safford The national southern terminus of US 191 is located at an intersection with SR 80 west of Douglas, in Cochise County. It heads north from this junction, past Bisbee Douglas International Airport and then through the unincorporated communities of McNeal and Elfrida before passing by Sunizona and the western terminus of SR 181, which provides access to Chiricahua National Monument. The road curves west and heads toward Sunsites, where it turns to the northwest and passes by the community of Cochise with a bridge over the Union Pacific Railroad. Continuing northwest, US 191 meets Interstate 10 at Exit 331, a trumpet interchange, and has a concurrency with I-10 for about . Heading northeast, I-10/US 191 passes around Willcox, with three exits serving the town: Exit 336, which is the southwestern end of the Willcox I-10 Business Loop; Exit 340, which is the northern terminus of SR 186; and Exit 344, which serves as the north end of the Business Loop.

Northeast of Willcox, US 191 leaves I-10 at Exit 352 and heads north toward Safford, leaving Cochise County and entering Graham County along the way. Just north of I-10, US 191 passes through an intersection with Page Ranch Road, officially designated as US 191 Wye. This provides a shortcut for traveling between Bowie and Safford, as the mainline of US 191 is curved toward the west near I-10. Going toward Safford, the eastern terminus of two state routes intersect the route, namely SR 266, which provides access to Fort Grant, and SR 366 in Swift Trail Junction, which climbs up to the summit of Mount Graham and provides access to Mount Graham International Observatory. Arriving in Safford, US 191 turns east at an intersection with 5th Street (US 70), where a concurrency with US 70 begins.

Safford to St. Johns Traveling east from Safford, US 70/US 191 passes by the communities of Solomon and San Jose before US 191 turns northeast to split from US 70. The route crosses the Gila River, then heads toward Three Way, passing through the Black Hills and entering Greenlee County. At Three Way, US 191 turns to the north, but the intersection is the northern terminus of SR 75, which heads toward Duncan, and the western terminus of SR 78, which heads into New Mexico toward Mule Creek. Heading north, US 191 is a divided highway for about until it arrives in Clifton, the start of the road's designation as the Coronado Trail Scenic Road (both an Arizona Scenic Route and a National Scenic Byway). This scenic road approximates the route Francisco Vázquez de Coronado took between 1540 and 1542. At the intersection with Zorrilla Street in Clifton, the US 191 designation temporarily ends and the road continues as US 191 Temporary through the Morenci mine.

At the northern end of the Morenci mine, the road reacquires its US 191 designation and travels through the Apache–Sitgreaves National Forest, in which it enters Apache County. The road through the forest is dangerous with no shoulders and many hairpin turns along steep mountainsides. The Hannagan Meadow Recreation Area is approximately from the National Forest boundary. Tourists driving the Coronado Trail often use this spot as a turnaround point, rather than continue north along the route. Occasionally, endangered Mexican wolves have been spotted visiting the region around the recreation area. About through the forest, US 191 arrives in Alpine and intersects US 180, where a concurrency begins. Continuing through the forest, the road travels through the community of Nutrioso before leaving the Apache–Sitgreaves National Forest. Just after leaving the forest, US 180/US 191 turns north at a T-intersection, the eastern terminus of SR 260. About to the northwest, US 180/US 191 enters Springerville and turns to the west at another T-intersection, this time with Main Street, where a triple concurrency between US 60, US 180, and US 191 begins. This triple concurrency passes through Springerville and ends about northwest of Springerville, where US 180/US 191 turns north and the road continues west as US 60. The US 180/US 191 concurrency continues north for another , intersecting former SR 81, which leads to Lyman Lake State Park before arriving in St. Johns as White Mountain Drive.

St. Johns to Utah

In St. Johns, US 180/US 191 intersects Commercial Street (SR 61), where the US 180/US 191 concurrency ends but a concurrency with SR 61 begins. This concurrency leaves St. Johns and travels north for about until SR 61 turns to the northeast and heads toward Zuni, New Mexico. Continuing north, US 191 immediately enters the Navajo Nation and then travels another until it arrives at Interstate 40 in Sanders. Here, US 191 has a concurrency with I-40 for from Exit 339 to Exit 333 in Chambers, where US 191 continues north through the Navajo Nation, intersecting BIA Route 28 in Klagetoh before its arrival in Ganado, where a concurrency with SR 264 begins. From there, US /SR 264 heads west past Hubbell Trading Post National Historic Site and toward Burnside, where the concurrency ends at a roundabout junction with US 191, SR 264, and BIA Route 15.

At the roundabout, US 191 travels north to Chinle, where it intersects BIA Route 7, which provides access to Canyon de Chelly National Monument. Continuing north, the route intersects BIA Route 59 in Many Farms, BIA Route 12 in Round Rock, and BIA Route 35 in Rock Point, before arriving at a T-intersection with US 160 near Mexican Water. Here, US 191 shares the route with US 160 for about until it turns to the north for its final in Arizona, leaving the state at the Utah state line and entering San Juan County, heading toward Bluff.

History

U.S. Route 191 (US 191) has existed since November 11, 1926. However, it did not enter Arizona at that time. US 191 didn't enter Arizona until June 15, 1981. The northern section of US 191 between Utah and Chambers was designated from two separate roads, one of which was already designated as State Route 63 (SR 63). The southern section wasn't designated as part of US 191 until June 1992, and was originally a section of U.S. Route 666 (US 666).

State Route 63 and BIA Route 12

State Route 63 (SR 63) was the original highway designated between Chambers and US 160 near Mexican Water. The SR 63 designation had been previously used by a different route through Petrified Forest National Park, which was decommissioned and handed over to the National Park Service in 1951. The later SR 63 was commissioned by the Arizona State Highway Department on January 10, 1961. When it was originally designated, SR 63 only ran from I-40 in Chambers (which at the time was also part of US 66) to the Navajo Nation boundary north of Chambers.

On December 14, 1962, the route from the Navajo Nation boundary to SR 264 in Ganado, which was maintained by the Bureau of Indian Affairs (BIA) as BIA Route 8 (BIA 8), became part of SR 63. The route from SR 264 in Burnside to US 160 (which was then designated as US 164) was originally part of BIA 8 and BIA 17 respectively. On June 15, 1970, BIA 8 and BIA 17 were transferred to the state of Arizona and designated as an extension of SR 63. Between Ganado and Burnside, SR 63 ran concurrently with SR 264. By 1981, SR 63 had a total length of .

The section of highway extending from US 160 near Mexican Water to the Utah state line, entirely within the Navajo Nation, was designated only as part of BIA 12, which continued north into Utah. Both the entirety of SR 63 and BIA 12 were approved by the American Association of State Highway and Transportation Officials (AASHTO) as a southern extension of US 191 on June 25, 1981. This extended the national southern terminus of US 191 from US 287 near Yellowstone National Park in Wyoming, to I-40 in Chambers. This also created a concurrency between US 191 and US 160 between SR 63 and BIA 12. As a result of the extension, SR 63 was decommissioned in favor of US 191.

As of 2021, the section of US 191 between US 160 and the Utah state line is still designated as part of BIA 12 and is still maintained by the BIA, and not by the Arizona Department of Transportation (ADOT). BIA 12 has a total length of between US 160 and the continuation of US 191 and BIA 12 at the Utah state line.

U.S. Route 666

U.S. Route 666 (US 666) was the original U.S. Highway designation between Douglas and Sanders. It was also an auxiliary route of US 66, from which US 666 derived its number. What would become US 666 was originally designated on September 9, 1927 as State Route 81 (SR 81) between US 80 in Douglas and US 180 in Safford. SR 71 was designated on the route between US 180 near Solomonsville and Clifton. Two further parts of the Douglas to Sanders route were sections of US 180 between Safford and Solomonsville and US 70 between Springerville and St. Johns. The remainder of the route between Douglas and Sanders was not part of the state highway system.

Undesignated parts of the Douglas to Sanders corridor were being added the state highway system beginning in 1928 when SR 71 was extended north from Clifton to US 70 near Springerville. On September 27, 1933, half of the route between St. Johns and Sanders was designated as part of SR 61. By 1936, SR 81 was designated over the entire route between US 80 in Douglas and US 66 in Sanders, with SR 71 being decommissioned. This established concurrencies with US 70 (which now took the former route of US 180), US 260 (which had taken over the original route of US 70) and SR 61.

Beginning in 1934, the Arizona State Highway Department petitioned the American Association of State Highway Officials (AASHO) to make the Douglas to Sanders corridor a southern extension of US 666. On December 4, 1938, AASHO approved an extension of US 666 from what was then its southern terminus in Gallup, New Mexico to Douglas, replacing the entirety of SR 81. Between Gallup and Sanders, US 666 was concurrent with US 66, entering Arizona at Lupton.

On November 7, 1974, the section of US 666 through the Morenci mine was redesignated as a temporary route, becoming US 666T. The intent was to construct a new section of US 666 around the mine to replace the old section. As of 2021, the proposed route hasn't been constructed but remains in planning. By 1988, the total length of US 666 in Arizona between Douglas and New Mexico was , not including US 666T.