You may have obtained this information elsewhere, since it has been a year since your posting. But I'll share what I know just in case it will help.
Mt. Zion Baptist Church is located at 4096 E. Cherokee Drive, Canton, Georgia 30115 and their phone number is (770) 479-3324. Founded in 1834, they will celebrate their 175th anniversary next month! Cherokee County didn't even exist until 1931, so Mt. Zion could be the oldest church in the county!
The church is located in the Hickory Flat community, which is located about six miles southeast of Canton. Across E. Cherokee Drive from the church, there is a cemetery that might even have some information you can use! My grandfather (who died before I was born)0 is buried there wih his first wife.