I looked through the resources available at the local library, but found little concerning Cantley Wallace Stewart.
The Warren County Marriage Index shows that he married Amanda A. Long on 2 February 1869.The marriage record is recorded at the courthouse in marriage Book C, page 36.At that point in time, little information was recorded regarding marriages beyond the couple's names and ages.
The couple was shown in the 1870 census of Young America (now Kirkwood).I didn't study the census records in depth, not knowing if you had already done that.
The estate of Amanda Stewart was filed on 22 August 1877 in Warren County, with J. C. Lockwood administrator.I am guessing that she may have been previously married with children.There was no other information given in the index regarding her estate.
From "The Past and Present of Warren County, Illinois - 1877", page 327, Voters and Taxpayers of Tompkins Township: "Stewart, C. W. physician; Kirkwood; Ind; from Kentucky."He was not listed in the 1886 Warren County album.
The 1880 US census entry for C. W. Stewart was the last sign I could find of Cantley in Warren County.Death records began in 1878, but was not strictly enforced until 1916.There is no cemetery or obituary listings found for him or either of his wives.
One item you might want to follow up on is Amanda's estate.It might include receipts for her burial, and give an indication of where that took place.Given that, there might be sexton's records for that particular cemetery which may or may not include Cantley.My hunch would be that he left Warren County to live with an adult child elsewhere.I wish I could have found something more specific for you.
Both the surnames Wallace and Stewart are common names in Warren County.Is it possible he was related to any of these others?Good luck with your search.