First, it is a old post office. I wasn't sure if it was still an active post office (according to USPS.gov it is not), but I found it intriguing. After all, Glens Fork has its own Zip Code, "42741.." It turns out that the building dates to 1932 and that the post office was reactivated in 1986 before its service was later discontinued again.
There is a lot of history to this unincorporated community in Adair County. A three-part history of Glens Fork (aka Glensfork, Glenville and Hardscratch) is interesting and informative. [Welcome Hamon, History of Glensfork, Kentucky, (Michael Watson, ed., Adair County Review, 1992-1993), available via Columbia Magazine]. The town was established by an act of the General Assembly in 1872 and it attempted to lure a Baptist College to town in 1874: "Glenville offers a thousand dollars to the proposed Baptist College, if it is located there." (Farmer's Journal, Nov. 11, 1874). The Baptists decided not to locate in Glens Fork, instead choosing Campbellsville for the site of its Russell Creek Academy (nka Campbellsville College).
At some point, the town's government dissolved and this community turned into a mere crossroads at the junction of KY-55 and KY-768.