Before it was known as Arp, this community on the Irwin-Ben Hill County line was known as Isaac. The name was changed sometime between 1910 and 1915, and judging by the burial dates in the adjoining cemetery, I would estimate that this church dates to about 1910.
Since there was already an Isaac Baptist Church, the small African-American community here named their church Mount Isaac, to distinguish it from the the white church. And though Arp is located in Irwin County, the church and cemetery are just over the county line in Ben Hill.
Many thanks to Laura Wiggins Norris for bringing it to my attention, and to Dale Bledsoe for the history.