The family story says William was the sheriff of Campbell County, Georgia. This is the county Union City is located, south of Atlanta. Campbell County was eventually dissolved and became Fulton County.
The problem and question about the family story is that a sheriff has jurisdiction over a county, not a city. A marshall has jurisdiction over a city. The following excerpt from “Acts Passed by the General Assembly of Georgia” 1908 references the differences of a sheriff and marshall in GA:

Acts passed by the General Assembly of GA 1908 referencing “Sheriff” and “Marshall”
According to his granddaughter Helen KEANUM, William “always carried a long muzzle pistol, about 18 inches long on his hip but never used it. He never killed anyone. He was described as a small man. His nick name was “Cabe”.
- William was born on the 27th of December 1856 in Campbell County, GA.
- His parents were Nancy Caroline STYLES and William Hampton HOPKINS.
- He married Mary Elizabeth COCHRAN on the 21st of March, 1876.
- He died the 21st of March, 1942 in Union City, Fulton County, GA.