"He represented the best of America; we're not going to see his like again," said singer-songwriter Kris Kristofferson, who wrote Cash's 1970 hit "Sunday Morning Coming Down."
More than 1,000 people attended the private two-and-a-half-hour service at First Baptist Church of Hendersonville, about 15 miles north of Nashville - the same church where Cash mourned the death of his wife, June Carter Cash, in May.
Cash, 71, died Friday of respiratory failure caused by complications from diabetes. He had been in declining health for years.
"I can almost live in a world without Johnny Cash because he will always be with us," said Cash's daughter, singer Rosanne Cash. "I cannot begin to imagine a world without Daddy."
Among the celebrities attending were country singers Vince Gill, Hank Williams Jr., Travis Tritt, Dwight Yoakam, George Jones, Ricky Skaggs, Ronnie Dunn, the Statler Brothers and the Oak Ridge Boys.
Other celebrities in attendance included rock-rapper Kid Rock, actress Jane Seymour - who worked with both Cash and his wife on "Dr. Quinn, Medicine Woman" - and former Vice President Al Gore, a native of Tennessee.
Kristofferson called Cash "Abraham Lincoln with a wild side" — a man always willing to champion the voiceless and downtrodden, "whose work in life has been an inspiration and salvation to so many people around the world."
The Rev. Franklin Graham - son of Cash's friend, the Rev. Billy Graham - called Cash "a good man who also struggled with many challenges in his life. He was a deeply religious man."
Emmylou Harris and Sheryl Crow sang the gospel hymn, "The Old Rugged Cross" and Bob Dylan's "Every Grain of Sand."
Cash, known as "The Man in Black" for his preferred attire, said in a hit song that he wore the color in honor of the poor and oppressed. He was buried in a black coffin with silver handles.
As the service came to end, country singer Larry Gatlin addressed his own son, Joshua Cash Gatlin, from the pulpit: "Son, this man fed your mama and me when we couldn't afford food. He paid rent for us when we couldn't pay rent."
For more than four decades, beginning in the 1950s as a peer of Elvis Presley in Memphis, Cash specialized in earthy songs about hard times and brooding love songs. His hits range from the rockabilly anthem "Get Rhythm," to the defiant but comical "A Boy Named Sue," to the recent "Hurt," about the ravages of drug abuse.
Cash rose to fame in his late 20s, but his career was nearly derailed by an addiction to pills. He credited his wife, June Carter Cash, whom he married in 1968, with helping him beat the addiction.
His commercial peak was from 1969-71 when he had a network television show with guests including Bob Dylan, Joni Mitchell and Kristofferson.
After a dip in record sales that lasted nearly two decades, Cash partnered with rock-rap producer Rick Rubin and recorded four critically lauded albums that found him a new, younger audience.
After his wife's death in May, Cash spent most of his time recording, leaving more than 30 songs yet to be released. He had planned to attend the MTV Video Music Awards shortly before his death, but couldn't because of illness. His video for "Hurt" won an award for cinematography at that show, and he has four nominations at the Country Music Association Awards in November.
Gatlin, Marty Stuart and producer Randy Scruggs were among the active pallbearers. Honorary pallbearers included Kristofferson; Rubin; singers Rodney Crowell and Willie Nelson; Marshall Grant, who played bass in Cash's original band; and his brother Tommy Cash.
A public memorial is being planned.