Walker was killed along with his wife and two of his band members when a van they were riding in ran off Interstate 65 south of Montgomery and overturned, state troopers said.
Killed in the wreck were Bettie Walker, 61; and Charles Lilly Jr. 44, both of Hendersonville, Tenn., and Daniel Patton Sr., 40, of Hermitage, Tenn.
Walker's grandson, Joshua Brooks, 21, also of Hendersonville, was injured in the accident. He remains in critical condition at an Alabama hospital, officials said.
The group was on their way back to the Nashville area after performing at a show near Gulf Shores, according to Tom Bowers, manager of the Hendersonville Funeral Home.
Bowers said family members have contacted the funeral home, which will be conducting services for the Walkers.
According to the Opry's Web site, Billy Walker was born in Ralls, Texas, and built an early career as the "Traveling Texan, the Masked Singer of Country Songs" and later shared the stage with Elvis Presley.
Walker joined the Grand Ole Opry in 1960.