Idaho

Franklin, settled in 1860 by sixty one Latter day Saint families moving north along the Bear River valley from Utah, is Idaho's oldest permanent Euro American town, and for its first twelve years nobody living there knew it was in Idaho at all. The settlers believed they were still within Utah Territory when they staked their claims, and Brigham Young himself visited the young settlement that June, naming it Franklin after the Mormon apostle Franklin D. Richards. Only in 1872 did an official government boundary survey fix the Utah Idaho line a mile south of the town, revealing that Franklin had been part of Idaho Territory from the start without anyone involved realizing it. The confusion says something real about how the Mormon settlement of southeastern Idaho actually worked, as a direct northward extension of the Utah colonization project rather than as a separate undertaking, moving along river valleys without much regard for a territorial boundary that had not yet been surveyed on the ground.

That extension left southeastern Idaho with some of the highest concentrations of Latter day Saints outside Utah itself, even though Pew's 2023-24 study finds no single tradition dominant statewide, Nothing in Particular leading at twenty two percent of adults ahead of Latter day Saint identification at fourteen.