The city directories on Ancestry.com. are an excellent source. The ones on Footnote.com are as well. However, there are other sites and locations to try.
The Hannibal Public Library has scanned city directories on its site, ranging from 1859 to 1929. Just as a fluke, I happened upon the site recently. They also have a scan of Stone's Tri-County Directory for 1892-93. This includes Adams County, Illinois, across the Missisippi River. Sure enough there was my ancestor, Bernard Dirks.
Lessons here: Libraries might have free digital images of some records.
And look at libraries outside your direct area of interest.