Counties you have been to that no other Atlasian has

[Sam Spade]

Washington County, Texas

I've been to Brenham before.  Many times.  Including the Blue Bell factory...    Not to mention Washington-on-the-Brazos.

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Been there to look at possibly buying a piece of property. 

[Sam Spade]

My family has a place in Gillespie County, TX - have to assume someone's been there and surrounding environs..  Let's try some weirder ones...

Union Parish, LA
Sabine Parish, LA
LaSalle Parish, LA (infamous)
(insert northern LA parish - and I don't mean driving through with these either)

Grant, NM
Catron, NM
Hidalgo, NM
(insert southern NM county - and I don't mean driving through either)

I've been to almost all counties in west Texas/Big Bend south and west of Midland/Odessa - let's try Culberson County and Brewster County (who's been to Big Bend). 

My east Texas list is pretty impressive too, but I haven't been everyplace.  Chambers County is a bit of an oddity.  How about Shelby County.  Once again, none of this is "driving through".