I have recently started researching my Knight and Spain famlies and in my research came across this info that sounds like it could be your family. In Hamilton Co. IL on 12/17/1854 a Jacob F. Spain married a Sarah M. Knight. Also on 1850 census for Hamilton co ther is a David D. Knight 54 born in NC with the following people
Mary 43 TN, James M. 21 TN, Sarah M. 15 IL, William C. 12 IL, Samuel R. 11 IL, Mary J. 9 IL, Louisa E. 8 IL and Captain A. 3 IL. Also in the 1860 Hamilton census there is a Jacob F. Spain 23 TN, Malinda 24IL (don't know if this is correct), Amanda E. 4 IL, John F. 3 IL, William M. 4/12 IL. Living right next to them is a Thomas Spain 51 VA, Polley 52 TN, William D. 17 TN, and George W. 15 TN. If you think this is your family let me know. I'm researching from James M. Knight, Sarah M. brother, and Alcenia Spain, the daughter of Thomas Spain. They would be my 6ggrandparents.