Let's watch the parade first:
Look at all those great businesses - Gridley Martz Insurance, Don's Drive-In Liquor, Vandel Furniture, Ethel's All Girl Bar and Lounge (bar AND lounge? So much drinking going on!). Keep going down the street, Canton Chow Mein Cafe, Ace Variety, Sansa's Cafe, Maytag District Store - lots and lots of easy leads to pinpoint where the parade happened, right? Wrong! I have not been able to find evidence of any of these businesses! Seriously - no one cared to remember and record Ethel's? That's ridiculous.
So the flags led me on a red herring, I thought this was Texas. I did find this remarkably similar footage of another centennial parade that happened in Kerrville:
Looks like we're on the right track, right? I don't think so... something isn't right, and not one of the floats are the same. The closest thing to a solid lead was the miniature horses in the last frame, the wagon has a banner from "Zip Feed Mills" which was a definite hit for Sioux Falls, SD, which was also celebrating it's centennial that year. We're on to something...
The Zip Feed Mill itself is an interesting structure, its construction started the year of this parade and it was the tallest occupiable structure until it became notorious in 2005 when its demolition ended up as a spectacular failed implosion:
Searching for a little more evidence, one more good lead, I found this picture of John Morrell's float:
That nails it! Those are definitely the girls in the first slide. This is Sioux Falls, 1956.
Research is fun, kids!