In the 1851 Canadian Census for Pickering, Ontario County, Canada West (Ontario) the family of Robert G. Barnum was enumerated as follows:
Robert G. Barnum, Waggon maker, b. Canada, No religion, 34 at next birthday, Male
Julian [sic] Barnum, b. Canada, 28 at next birthday, Female
Chas. E. Barnum, b. Canada, 2 at next birthday, Male
Lydia Ann Barnum, b. Canada, 1 at next birthday, Female
In the 1861 Canadian Census for Pickering Township he is listed as a millwright and a Hannah Matthews, b. Québec, age 62 was living with the family. Robert does not appear in the 1871 Census, nor does Julia Ann. A possible explanation is that in the 1860s and 1870s free land was given to men from Ontario who would go and settle in Michigan. He may perhaps be found there.
Other sources show his birthplace as Fairfield County, Connecticut and also as New York.
The family bible gives his death date as 24 October, while the Illinois Statewide Death Index says 21 October.