The “Challenge” is to find a cache in 200 different
counties across the US. Any type of cache, in any state, can be
used to help you meet the qualifications.
You will need to provide a form of evidence that you have
qualified for this challenge: either a US County map (or a computed
statistical output) generated by a geocaching statistic application
and displayed on your profile page; or a list of counties with a GC
number that you have found in each of the counties on your list.
The list can be accomplished by creating a public shared bookmark
list on this cache page, or by typing the list as part of your
“found it” log entry. I think the easiest way to
provide the required evidence is to use the stats generator found
at mygeocachingprofile.com.
Below is an example of the US County output that it provides.

The application is easy to use and uses your “my finds”
pocket query to do all the number-crunching for you. You can easily
copy-paste the HTML output into your profile page for all to see,
or you can do a screen-capture of the output and add it to the
photo gallery of this cache page by adding the image to your
“found it” log.
The actual D/T rating of this hide is about a 1/1.5. The listed
D/T rating is based on qualifying for the Challenge.
Good luck and have fun!
Congrats to MCP for being the FTF!