Hmmm. Well if you are visiting Sheboygan County, WI, I have a bookmark list for you.
In all seriousness, though, I imagine you could sort caches you downloaded by placement date using a third party program. I think I recall lurking a recent thread about determining county boundaries and the resolution was that GSAK could do it. I wouldn't know though. I currently use a mac, and I don't bother playing around with MacCaching. I did my list by seaching from the center and selecting old caches within the county by hand.
Of course there's always the chance someone has done the work for you. If you know one oldest active there already, you should definitely check its bookmark lists first. EDIT: Umm I can't read. You already tried that.