Jairus Cassius Fairchild (December 27, 1801 – July 18, 1862) was an American Democratic politician and a businessman.

Fairchild had business interests in cranberries and the lumber industry and was president of the Watertown-Madison Railroad Company.

In the referendum to ratify the Wisconsin Constitution in 1848, a concurrent election took place to choose the first state officers.

Lucius and Cassius both achieved the rank of Brigadier General, serving with the Wisconsin Volunteer Infantry.

[citation needed] Jairus C. Fairchild died in Madison on July 18, 1862, and was buried at Forest Hill Cemetery.