Chapin and his wife, Camille, both grew up in the 110th District. Upon graduating Charleston High School, he enrolled in and received a bachelor’s degree from the University of Illinois. He is also a graduate of the University of Illinois College of Law. Before being elected to the legislature, Chapin served as a Senior Assistant State's Attorney in Champaign County.
Chapin and Camille are members of Faith United Methodist Church. They have four children: Jack and Annie and twins, Kyra and Grace.