Natrona County is listed as #1
Reason given is that at the time land values were represented by each county plate number.
Natrona (as I understand it anyway) was considered to have the highest land values when the county plates were dispensed.
You win the daily History Award....
The whole Tea Pot Dome area is a bit of a sight blight from my visit there some years ago to document a USHCN weather site for WUWT Anthony Watts.
I see no shortage of NE Wyo. County plates running along US16.
As always, YMMV...