Bradley County Chief Deputy Wayne Bird died early Friday, just two weeks after going on medical leave.
Sheriff Jim Ruth announced the death in an email.
"It is with deep sadness that I announce this morning that Chief Deputy Wayne Bird passed away early this morning," Ruth wrote.
"Chief Bird will be greatly missed by his family and friends. Needless to say he will also be missed by the men and women of the Bradley County Sheriff's Office.
"He brought a great deal of experience and expertise to the sheriff's office," Ruth wrote. "We in Bradley County owe a great deal of gratitude to him for the professional and moral leadership that he brought to his position of chief deputy."
On March 14, Ruth announced that Bird had "been stricken suddenly with a critical illness" and would go on leave.
He didn't say what the illness was, but the Cleveland Daily Banner quoted Bird's brother, Doug Bird, as saying he had melanoma, a type of skin cancer, and his condition was terminal.
Bird, a Florida law enforcement veteran, had served as chief deputy since 2010.
Last year, he took the helm of the department for several weeks in May and June while Ruth recovered from a brain-stem stroke he suffered May 30 in Nashville.
Another Bird brother, Don Bird, a former two-term Tennessee House member, managed Ruth's campaign for sheriff.
Wayne Bird is survived by his wife, Colleen, and sons, Sterling and Richard.
Funeral arrangements will be announced.