The singer who recorded the song We Are Family with her sisters, has died at the age of 60.
She was found in her home in Arizona by a friend on Friday.
A statement on the Sister Sledge Facebook page says: "Yesterday, numbness fell upon our family. We are saddened to inform you that our dear sister, mother, aunt, niece and cousin, Joni passed away yesterday.
"Please pray for us as we weep for this loss. We do know that she is now eternally with Our Lord.
"We thank you in advance for allowing us the privacy to mourn quietly as a family. We miss her and hurt for her presence, her radiance, and the sincerity with which she loved and embraced life."
Tributes have poured in from with the world of music.
Chic star Nile Rodgers wrote on Twitter: "#RIPJoniSledge #WeAreFamily My heartfelt condolences to your family because they are my family too. We did something pretty amazing together."
La Toya Jackson also paid tribute to the singer, saying: "So sorry to hear that Joni Sledge has passed, my condolences to her family, friends and love ones. #Sistersledge we are family! #RIP.