The Union County, Illinois census in 1860 shows:

William C. Sparks      age 46               TN
Sarah R.                    age 39               TN
Nathan S.                  age 10               TN  
Mary E.                     age 8                AR
William                      age 7                AR
Robert                       age 5                AR   

( My Great grandfather, Robert Donnell)
also listed are 2 laborers: James Gere age 28 who could neither read nor write, and John D. Bolberry age 38.
 

William's brother, Martin Sparks, had moved his family to Illinois briefly in about 1837 but returned within two years to Tennessee. 

William's sister Mildred Sparks Edwards was in Saline county, Illinois when she died in 1873. Saline is located in the far southern part of Illinois very near Union county, but as yet, the Edwards have not been located on the census records for 1860 or 1870 in Illinois.

William C. and family remained in Illinois until about 1862 when they moved farther south, landing for only a brief period in Kansas.