Diamond Rio is an American country music band from Nashville, Tennessee. The band consists of Marty Roe (lead vocals, guitar), Jimmy Olander (lead guitar, banjo), Dan Truman (keyboards), Dana Williams (bass guitar, vocals), Micah Schweinsberg (drums), and Carson McKee (fiddle, mandolin, vocals). The band was founded in 1982 as an attraction for the Opryland USA theme park in Nashville, Tennessee, and was originally known as the Grizzly River Boys, then the Tennessee River Boys. It was founded by vocalists Matt Davenport, Danny Gregg, and Ty Herndon, the last of whom became a solo artist in the mid-1990s. After undergoing several membership changes in its initial years, the band held the same membership from 1989 to 2023, which consisted of Roe, Olander, Truman, Williams, Brian Prout (drums), and Gene Johnson (fiddle, mandolin, vocals). After the latter two retired in 2022, they were respectively replaced by Schweinsberg and McKee.

Diamond Rio was signed to Arista Nashville in 1991 and debuted with the single "Meet in the Middle", which made them the first band ever to send a debut single to No. 1 on the Billboard Hot Country Songs charts. The band charted 32 more singles between then and 2006, including four more that reached No. 1: "How Your Love Makes Me Feel" (1997), "One More Day" (2001), "Beautiful Mess" (2002), and "I Believe" (2003).

Diamond Rio has recorded nine studio albums, four Greatest Hits compilations, and an album of Christmas music. Three of the band's albums have achieved RIAA platinum certification in the United States. In addition, Diamond Rio has received four Group of the Year awards from the Country Music Association, two Top Vocal Group awards from the Academy of Country Music, and one Grammy Award. The band is known for its vocal harmonies, varied instrumentation, and near-exclusive use of only its own band members on recordings instead of session musicians. Their sound was originally defined by mainstream country, bluegrass, and rock influences, but later albums drew more influence from Christian country music and country pop.

In 1982, Matt Davenport and Danny Gregg founded a band at Opryland USA, a former country music-based amusement park in Nashville, Tennessee. The band was first named the Grizzly River Boys, after a new river rafting ride at the park, but quickly changed names to the Tennessee River Boys due to its members disliking the original name. Originally intended to promote the park through a one-time television special, the band proved popular enough that it became one of many regular performers there. Davenport, Gregg, and Ty Herndon alternated as lead vocalists, with Davenport also playing bass guitar and Gregg on rhythm guitar; completing the lineup were Larry Beard (lead guitar, fiddle, banjo), Mel Deal (steel guitar), Al DeLeonibus (piano), and Ed Mummert (drums). The group "swapped lead voices, told jokes, and balanced old-school country concert shtick with a contemporary sound". Herndon left the group in 1983 to compete on the talent show Star Search, and became a solo artist for Epic Records between 1995 and the early 2000s. Herndon was temporarily replaced by Anthony Crawford and then Virgil True before his role was taken over by Marty Roe, who had originally toured nationally with the Christian band Windsong, and worked in the park by doing impersonations of Larry Gatlin. Following Herndon's departure, DeLonibus and Mummert quit as well, with Dan Truman (who had previously played in Brigham Young University's Young Ambassadors) and Jimmy "J. J." Whiteside taking their places. Beard quit shortly afterward and ultimately became a session musician, and former Mel McDaniel sideman Jimmy Olander took his place. The band, through the assistance of Bill Anderson's drummer Len "Snuffy" Miller, submitted demos to various Nashville record labels with no success.

By 1985, the Tennessee River Boys had quit working at Opryland. According to Roe, while the band enjoyed playing at the park, they also felt that their status as a theme park attraction discredited them as "real musicians" to those in the Nashville community. For the next few years, they played at small venues, such as high school auditoriums, and usually worked no more than four concerts a month. They also competed on Star Search, but were eliminated in the first round. Frustrated by the sporadic touring schedules, Whiteside quit the group and was replaced by Brian Prout, who previously performed in Hot Walker Band and Heartbreak Mountain. Around 1986, Deal and Gregg both left the group, the latter due to health complications from a serious illness he had developed as a teenager. They initially chose to operate as a quintet, with Davenport as the sole lead vocalist and Roe and Prout singing harmony; when this arrangement proved unsuccessful, they found mandolinist Gene Johnson, a former member of the bluegrass group Eddie Adcock's IInd Generation, which Olander was a fan of as a child. Johnson debuted at a concert in Clewiston, Florida, in May 1987. Also at this point, the band members supplemented their incomes with outside jobs: Johnson continued to work in carpentry, Olander and Roe mowed lawns, and Prout drove tour buses.

In 1988, the band caught the attention of Keith Stegall, a singer-songwriter who would later become known primarily for his work as Alan Jackson's record producer. Stegall produced demos for the Tennessee River Boys, but noted that Davenport could not record the lead vocal and bass parts at the same time, as they would be difficult to separate in the control room. As a result, Stegall had Roe sing a "scratch" vocal track live with the other musicians, which would then be replaced by Davenport's voice in post-production. Upon hearing Roe sing the "scratch" track, Stegall successfully convinced the other members that Roe should be the lead vocalist instead. Due to his discomfort outside the lead role and his wife's dissatisfaction with his career, Davenport quit in late 1988, becoming the last founding member to leave. The group quickly had to find a replacement, as they were scheduled to appear on the talk show Nashville Now on January 23, 1989. Alan LeBeouf, who had just left Baillie & the Boys, expressed interest in replacing Davenport but ultimately declined due to other commitments. They finally chose Dana Williams, a nephew of the bluegrass group Osborne Brothers and former sideman for Jimmy C. Newman, who had been a fan of the Tennessee River Boys since Herndon was a member.

Williams officially joined before the Nashville Now appearance, but the band still did not have a record deal at this point. They continued to record demos in Prout's garage with assistance from Monty Powell, who had previously hired Roe and Olander for recording jingles, but wanted to produce commercial music. Powell was a friend of audio engineer Mike Clute, who would later become one of the band's producers, and songwriters Tim DuBois and Van Stephenson. DuBois was talking with record executive Clive Davis about creating a country music branch of Arista Records called Arista Nashville; Stephenson would later sign to the label in 1993 as a member of Blackhawk. Initially, DuBois was hesitant about signing the Tennessee River Boys, as he felt that there were too many popular bands in country music, and he was about to sign both Asleep at the Wheel and Exile. He expressed interest in signing Roe as a solo artist, but at Powell's insistence, he agreed to see the band open for George Jones at a May 1989 concert, and officially signed them to Arista Nashville in 1990. The band members also decided to choose a new name, as they thought that Tennessee River Boys sounded more suitable for a bluegrass or gospel group than a country one. Among the names they had chosen were Kilroy and T-Town Mavericks, the latter of which was rejected by Arista executives. Prout suggested Diamond Rio, after the truck manufacturing company Diamond Reo Trucks. The name had been previously rejected by another country band, Shenandoah, whose lead singer Marty Raybon (also a former member of Heartbreak Mountain) gave Prout permission to use the name even though Shenandoah "conducted business" under that name.

Shortly after the band received its record deal, the band underwent a series of misfortunes when Olander, Johnson, and Williams came down with health problems. On August 9, 1990, Johnson was injured in a carpentry accident in Arkansas a day before his 41st birthday, severely cutting his left thumb. Robert Bolin substituted for Johnson during the band's tour in Brazil with Kevin Welch and Jann Browne. On September 6, four weeks after Johnson's accident, Williams was water skiing with his family in Cookeville, Tennessee, as his boat came forward at high speed when his wife was picking him up. The propeller slashed Williams' legs, and he was rushed to a hospital for his injuries. Brian Helgos and Paul Gregg (Danny Gregg's brother, and a member of Restless Heart) substituted for Williams. Meanwhile, Olander discovered that he had a lemon-sized tumor that was pressing against his esophagus. The tumor was never successfully diagnosed, although it ultimately vanished.