Yvette,

Have you looked on FamilySearch? It's a free internet site with the 1880 federal census. In a quick search I found two boys named Isiah Mitchell in Charleston County, SC and one named Isah Mitchell in Beaufort County, SC.

If your local library subscribes to HeritageQuest, you can search for him in other census years. In the 1910 census I found an Isiah Mitchell, 37, laborer at a mill in Charleston, SC.

Best wishes.