- Founded as "Boston" (March 1855)
- Renamed Manhattan (June 29, 1855)
- Incorporated (May 30, 1857)
- Establishment of the Kansas State Agricultural College, present-day Kansas State University (February 16, 1863)
In March 1855, settlers organized by New England Emigrant Aid Company (NEEAC) founded the Free-State town of Boston, Kansas, which was renamed "Manhattan" on June 29, 1855. As with other NEEAC settlements, the town's purpose was to bolster the Free-State cause by expanding the number of antislavery voters in Kansas Territory. Prior to Manhattan's founding, the settlement of Manyinkatuhuudje (translated to Blue Earth Village) had been a home of the Kaw, or Kanza, American Indian tribe on the Big Blue River. With the Kansas-Nebraska Act in 1854, white settlers entered the area in the fall, first following George S. Park (also the founder of Parkville, Missouri and Park University in the Kansas City metropolitan area). Park's settlement on the Big Blue River, called Polistra, was the first white settlement at the site, and it was soon joined by a neighboring settlement called Canton.
Neither of those settlements expanded significantly prior to their joining with the new settlement of Boston in March 1855. In June of that year, a steamboat wrecked on the Kansas River, and the passengers, mostly from Ohio, settled at Boston and requested the name change to Manhattan. During Bleeding Kansas and the Civil War, Manhattan benefited from its distant location from the volatile Missouri-Kansas border and its close proximity to Fort Riley, both of which helped prevent violent proslavery raids against the town. Early on, Manhattan benefited from travelers who purchased supplies before continuing on their journey further west. On February 16, 1863, the state legislature established the Kansas State Agricultural College, which is today Kansas State University and one of the defining aspects of the city. In 1866, the Kansas Pacific Railroad opened a route through Manhattan, and the city's economic future was secured.