Robert Ferguson married Ellen Stanton on 22 April 1861 in St. Louis. The original record may name the parents, especially if they had a church wedding. 1870 US Census has children named Mary, William J., Ella and Emma, but wife named Anna. William will be the name of either Ellen/Anna's father or of Robert's father.
The 1880 census has wife's name as Ellen. Another child,
Julia, has joined the family. He is a carpenter. I do not believe he is the same Robert Ferguson who shows up as a stone mason in the same census. It would be unusual to have two trades.