The smallest population state is Wyoming, which had a population of 563,626 according to the 2010 census. The same census said the seven counties in NE Colorado (Weld, Logan, Morgan, Phillips, Sedgwick, Washington and Yuma) had a total population of 322,126 — with Weld County accounting to over 78% of the total.
The Nebraska panhandle would probably love to team up with them that would add I think about 100K and maybe siome of maybe utah as well...
Utah's over on the other side of Colorado. Wyoming doesn't have any population too spare, so it would be up to the Nebraska panhandle and Western Kansas to make up the deficit.
There's a whole lotta nuthin' out there...