Jairus Cassius Fairchild (December 27, 1801 – July 18, 1862) was an American Democratic politician and businessman. He was the first State Treasurer of Wisconsin and the first Mayor of Madison, Wisconsin. He was the father of Wisconsin's tenth governor, Lucius Fairchild. In historical documents, he is often referred to as "J. C. Fairchild" and his first name is sometimes misspelled "Jarius".