I also have a copy of the actual marriage certificate that shows that date.
The Gallemore Cemetery listings show these burials (both wives of Erastus): Mary M Hoskinsw/o E.1 Aug 1841 - 22 Apr 1878 R. Matildaw/o E.6 Apr 1840 - 19 Oct 1898
GALLEMORE Cemetery ( Volume III page 95) SW1/2 Section 26-Lima "W" Township north of Marcelline,IL.
You will note that Erastus' wife is listed as "Rachel" in the 1880Census, and R. Matilda on the tombstone.I think she may have switched her name around some in later years to reduce confusion with another Matilda/Mattie Gallimore who ran into trouble with the police.
In addition to the question about Nora's age, I note that "Emmet" is age 10 in the 1880 Census...and I find his birthdate in other websites as older than that.