The directory on DavE's disks that I found these in suggested they might be from the 1988 Fallcon. They aren't; that was Consensus*, and the badge for that is online, and it does not match the badges people are wearing in these pictures.
But pretty clearly a convention in Minneapolis. Can anybody pinpoint the hotel? Does that limit what nearby years it could be the fallcon from? Or the badges? I've checked a few years each direction and only some have badges online, but the ones I've found online clearly don't match these.
* With Don abstaining.