The exact number of affected residents is unknown, though one county has more than two dozen misaddressed residents. Also unclear is why Missouri residents were assigned Iowa postal addresses in the first place. McCaskill’s letter said it appears to have something to do with mail delivery routes along the sparsely populated area where the two states come together, though local residents were never given a good explanation…

The quirk also makes voter registration difficult because Iowa addresses aren’t recognized in Missouri’s voting system.

“We always put their address as the courthouse address,” Church said of the 30 or so Clark County residents with Iowa addresses. “It has to be a Missouri address to have a voting district.”