Welcome to Silver Bay, Minnesota!
This little town 60 miles northeast of Duluth on the shores of Lake Superior seems to have it all. It even has... MYSTERY!
https://www.topozone.com/minnesota/lake ... ver-bay-2/
It's a bit small for the suggested town size, but I think it'll work. Perhaps we can assume that the town is a bit bigger than the map shows, given the additional population required to work at the DART facility.
In "the 80s that never were" the taconite mining facilities were never built. Instead, the town was created in the 50s specifically because of the Loop. The facility is located on what in our world is the taconite tailing ponds, and the industrial buildings nearby are the DART lab(s). The hills in the area contain some other element useful to DARPA and the DART project, and the tiny little community of Silver Bay joined the ranks of the Malaren Islands, the Norfolk Broads of England, and Boulder City, Nevada (and perhaps other places) in being the location of the technological marvel that is the Loop.