Fans from all over the country have written to say how deeply the song has touched their lives, said Tim Womack, the group's electric guitar player.
"You can see the power of music to help heal," he said.
The song is even more poignant because it's a true story.
"Leaving October" was co-written by his brother, Drew Womack, the group's lead singer and acoustic guitar player, and the person in the song was a friend.
Since the album came out last year, most of the band's fan mail has been about that song, and people have been sharing their experiences, said Tim Womack, 29.
"They'll say things like 'I lost my mom, and this has really helped me get through it'," Womack said.
"Whatever Comes First" and the band's second hit, "Hand of Fate," also have inspired listeners to write.
Sons of the Desert steadily has been gaining fans, with some saying they never really listened to country before, Womack said.
Other Sons members are bass guitar player Doug Virden, 27; keyboardist Scott Saunders, 32; and drummer Brian Westrum, 34. Drew Womack, 27, co-wrote most of the songs on the band's first album.
Through years of playing clubs and honky-tonks, the Texas-based group kept its own format and playlist.
"A lot of bands were playing Top 40, and we did our own thing," Tim Womack said.
Sons of the Desert established its sound and headed to Nashville, Tenn., where the group was booked to perform at The Wild Horse Saloon for a few weeks. After the third night, Sons of the Desert had gained a national management team, a music publisher and a deal with Epic Records.
If you think that sounds like something out of a movie, you're partially right.
The group gained its name from a 1937 Stan Laurel and Oliver Hardy film.
The members had a show coming up and needed a name. Someone stopped in a movie store and saw "Sons of the Desert" on the shelf, Womack said.
The experience has turned the musicians into movie buffs.
"We all have a copy of the movie now," he said.
The Sons, their wives and sons have moved to Nashville. Tim Womack and his wife, Brita, have a 3-year-old named Eric; Scott and Donna Saunders are the parents of 5-year-old Brandon; and Doug and Bridget Virden are expecting a baby in April.
The musicians are writing songs for their new album and plan to return to the studio in March.
Womack said he and his bandmates share the same tastes and make decisions quickly.
"We don't butt heads too much; we pretty much all have a vision of where it's going," Womack said.
The Sons toured with country entertainer Tim McGraw for four months in 1997, and the group is firming up plans to go on the road this year.
Womack admits he's a little awestruck when he looks to the future and considers the possibilities.
"My gosh, to be given this chance and to be here is incredible," he said.