The Dexter swamp lights

On 20 March 1966 a farm family and others near Dexter, Michigan, reported a glowing object over a swamp. An Air Force consultant later pointed to swamp gas.

On Sunday 20 March 1966 deputies took reports of an object coming down in a wooded swamp in Dexter Township. A truck driver named Frank Mannor told police that he and his son had walked into the swamp. In the police report he is quoted describing a whistle, like a bullet ricocheting off something. Then, he said, the object climbed, flew directly above them and disappeared.

A later retelling gives the family's view from the house. The Mannors saw a red glow resembling a shooting star sink toward the trees on the northern side. It stopped, hung over the family's trees and shifted through blue and then white.

Wikipedia counts this as the first of two mass sightings in Michigan, on the nights of 20 and 21 March 1966. The second came near the Hillsdale College arboretum, about 50 miles away. J. Allen Hynek, a civilian investigator for the Air Force, attributed the reports to swamp gas, an explanation that was widely mocked.