This was in reference to the ridge that forms the watershed divide between the Missouri and Mississippi rivers.

The town officially became known as Adair on August 20, 1872, when it was incorporated with the county.

Adair was the scene of the first successful train robbery in the American West when on July 21, 1873, the James-Younger Gang (led by Jesse James) took US $3,000 from the Rock Island Express after derailing it southwest of the town.

[5][6][7][8][9] Adair is recognizable from Interstate 80 by its tall yellow "smiley-face" water tower.

Its roadsign warmly greets visitors with, "Welcome to Adair; it'll make you smile".

Some of the local businesses incorporate the smiley-face tower image into their company logos.

Adair is mentioned in the 2013 Stephen King novel Doctor Sleep.

In February 2024, Adair Police Chief Brad Wendt was convicted on 11 of 15 federal charges, for conspiring to make false statements to the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and illegal possession of a machine gun.

"Authorities say he bought machine guns for the police department, then sold them for an almost $80,000 personal profit.

There were 396 housing units at an average density of 178.8 per square mile (69.0/km2).

38.8% of all households were made up of individuals, and 19.4% had someone living alone who was 65 years of age or older.

39.1% of all households were made up of individuals, and 21.0% had someone living alone who was 65 years of age or older.