On June 29, 1861, after Virginia voters approved secession, other delegates expelled them from the convention, and replaced them with secessionist Preston County lawyers Robert E. Cowan and Charles J. P.

[4] Nonetheless, Kingwood voters elected McGrew as their mayor, and voters of Preston and surrounding counties elected him to represent them in the newly created West Virginia House of Delegates alongside Zinn after West Virginia was admitted to the Union.

McGrew also was managing director of the West Virginia Insane Hospital for four years during and after the American Civil War.

McGrew survived his wife by nearly two decades and lived to see his sons begin their careers in public service.

In 1989, the James Clark McGrew Society was formed to foster understanding of this founder of West Virginia.