WILSON, ROBERT *** CLINE, NANCY09/02/1866 00B/0180 00006848 KNOX
That's Book B, Page 180, Certificate #6848 Knox County.
1870 US Census - Walnut Grove Township, Knox County, Illinois NA Series: M593Roll: 241Page: 487Sheet: 16Date: 11 August 1870D/F: 115/103 Peter "Hallenbeck", 30 M W Farmer --- $3000 NY Robert Wilson, 28 M W Works on Farm $800 $150 NY Nancy Wilson, 24 F W Keeps House IL Jacob "Hollenbeck", 24 M W Farmer $1500 $800 NY Peter Neilson, 20 M W Work on Farm Sweden
This seems a bit strange.Robert is shown as owning property, but living in another's household.Then, the Wilson's were placed in between the two Hollenbeck's.
Just a guess - the best match for Robert from the 1860 census index that I could find was the son of a Robert Wilson born in Scotland, and living in Lee County, Iowa.Lee County and Knox County were connected by rail at this point, and it is common to find people drifting back and forth.The distance may be no more than 40 or 50 miles, or an hour or so by rail.
I couldn't find any likely matches for Nancy in the 1860 census index.I couldn't find a match for Robert and Nancy in the 1880 census, even using the LDS search engine that will find couples.
Did you have any more clues to link them to Warren County?