Paul, don't know if this will help, I found this on familysearch.com that has an 1880 census lookup. I couldn't find any Olof/Olaf/Ollie/etc Erickson/etc married to any Martha in Illinois. Possibly is a different spelling. I tried various ones. Just type Illinois Statewide Marriage Index in your web browser and the site shoud come up.
Hope this helps. Kathy P
1880 Moredock, Monroe Co, Illinois Census name relationship married/single sex race age birth/dad/mom
F. STRATHMEIER Self M Male W 29 WESTFALEA Farmer WESTFALEA WESTFALEA Anna STRATHMEIER Wife M Female W 26 IL Keeping House HANOVER HANOVER William STRATHMEIER Son S Male W 11M IL At Home WESTFALEAIL H. HILDERBRAU Son S Male W 6 IL At Home WESTFALEA IL Ollie ERICKSON Other S Male W 30 SWEDEN Labor SWEDEN SWEDEN Fritz KASSENS Other S Male W 30 HANOVER Labor HANOVER HANOVER Harry HUGHES Other S Male W 22 MO Labor MO MO Fritz TAELIR Other S Male W 24 BREMEN Labor BREMEN BREMEN