Several years back, an excellent book by Dennis Kitchen came out called Our Smallest Towns: Big Falls, Blue Eye, Bonanza, & Beyond. It was a photo essay chronicling the smallest town in each of the 50 states. For each town, he assembled all of the residents, or as many as could show up, to pose for a photograph. It also included a small write up about the town from one of its residents or dignitaries. Whether the town has 2 people or 200, the photos are fantastic! I highly recommend checking out this book for yourself.
I bring this up to point out, of course, the entries for the Great Plains states. The Great Plains is dotted with countless small towns, some of them very small, and many of them getting smaller all the time. Below is a list of the smallest towns (as far as the aforementioned book is concerned) in each of the Great Plains States:
Montana: Ismay (pop. 20) – A particularly wonderful photo with the full sweep of the Great Plains in the background was the shot for the book for this town. This town also lies extremely close to where the proposed trail will run! It was also once unofficially called Joe, Montana! No joke.
North Dakota: Hove Mobile Park (pop. 2)
Wyoming: Lost Springs (pop. 3) I’ve been there!
South Dakota: White Rock (pop. 6)
Nebraska: Monowi (pop. 8) – Monowi earned the cover shot for the book, and apparently has but one resident remaining, according to the 2010 census.
Colorado: Bonanza (pop. 8) – Not in the Great Plains portion of the state, and has been apparently “taken over” by the town of Lakeside as the least populated.
New Mexico: Grenville (pop. 30) – My absolute personal favorite photo from all of the states – a must see photo if there ever was one.
Oklahoma: Hoot Owl (pop. 0) – There are now 4 people living there.
Total (just for fun): 115
The Great Plains Trail 
There is (or was?) a very small town near my hometown called Little Joe Montana. This was long before the 49ers won their first Superbowl.
You’ll have to go back and see what’s still there. I remember when they “changed” the name. At first, I thought it was official, but apparently, it was more of a publicity stunt.