And the map continues to fill in! Wisconsin (and other upper midwest states) were historically strong hotbeds of independent grocers, so the chain lists for La Crosse and Eau Claire are probably shorter than average for cities of their size.
In La Crosse, the 1950s Kroger at 2600 Slate Road survives in spite of some gingerbreading on the facade. It stands next door to a modern Festival Foods store, and the size differential between the two structures
really drives home how supermarkets have exploded over the last six decades:
A 1950s Piggly Wiggly at 66 Copeland Avenue survives in completely original condition.
124 6th St N (a National in the 1940s) is very eye-catching, although it doesn't look much like a supermarket. On Street View, the facade bears faint labelscar from a different (presumably non-grocery) tenant.
Eau Claire sports a decently-intact 1950s Red Owl at 1417 South Hastings Way, though the original protruding sign and canopy appear to have recently been removed from the structure. Many Red Owls were independent franchises, however, so they didn't have chainwide-consistent designs.
Oh, and another thing: I'm interested to see that National persisted in the Eau Claire listings through 1960 and beyond. National disappeared from the Manitowoc directories by 1950, so this indicates they spent mid-century paring back their presence in northern markets without withdrawing from them completely.