In 1855, Denison was convinced by his brother-in-law, Isaac Goodnow, that he should move to Kansas Territory to help establish a new town for the New England Emigrant Aid Company. On March 13, 1855, Denison joined a party of Company members leaving Boston, and made his way to Kansas Territory, which was soon to boil over with violence. (See Bleeding Kansas.) Over the next several years Denison was part of a small group that settled and built the abolitionist town of Manhattan, Kansas, at the union of the Kansas River and the Big Blue River in the Flint Hills.