In the 1880 census, they are in Fountain Green, Hancock Co., Illinois, and the data suggests they were not married in Illinois, and he may have been born as early as 1825:
Campbell, Jacob, 55 [b 1825]... farmer, [b] Virginia of Virginia-born parents
Margaret, 44 [b 1836], wife, born Virginia of Pennsylvania-born parents
John H., 24 [b 1856], son, at home, born Virginia... suggesting that Jacob and Margaret were married in Virginia OR that Jacob had an earlier wife, mother of this John.
David, 15 [b 1865], son, at home, born Virginia
C. Elizabeth, 14 [b 1866], daughter, at home, born Indiana
Jacob, 12 [b 1868], son, born Illinois
Ida, 7 [b 1873], dau, born Illinois
Margaret, 5 [b 1875], dau, born Illinois