On the night of August 21, 1955, a gathering of friends and family at a farm in Christian County, Kentucky was interrupted by the appearance of several small, humanoid creatures in the backyard.
After a series of failed attempts to shoot the creatures and chase them away, the families locked up the doors and hid inside for the rest of the night. The creatures continued to harass the group until sunrise the next morning. After this, they were never seen again.
Though Air Force Project Blue Book never conducted an investigation, the strength of the evidence for the Kelly-Hopkinsville encounter makes it one of the most convincing cases of extraterrestrial contact in UFO history.