The problem is that the book listed Pekin as "Perkin". It also lists my old home town, Poughkeepsie, as "Paughkeepsie". Otherwise the book is very helpful. It lists the dates the post offices were in operation, name changes (of which there were a bunch), county, and geographic coordinates. Only two spelling errors found so far, but I am a stickler for accuracy in historical research, and I guess from now on I'll never be completely confident in this book.
Anyway, amend my post above regarding "Perkin" in Johnson County, to Pekin.