The Union Colony of Colorado (also called the Greeley Colony and The Union Temperance Colony) was a 19th century U.S. private enterprise formed to promote agricultural settlement in the South Platte River valley in the Colorado Territory. Organized in October 1869 by Nathan Meeker in order to establish a religiously oriented utopian community of "high moral standards", the colony was founded the following year at present-day Greeley, Colorado, which was established by the colony in March 1870. It was financed and promoted by New York Tribune editor Horace Greeley, a prominent advocate of settlement of the American West. The colony greatly advanced homesteading and irrigation usage in present-day northern Colorado, demonstrating the viability of cultivation at a time when agriculture was emerging as a rival of mining as the basis for the territorial economy.
Horace Greeley had journeyed west in 1859 at the height of the Colorado Gold Rush, going from Denver to Fort Laramie via the Overland Stage before continuing west to California. Greeley's route took him up the valleys of the South Platte and Cache la Poudre near the eventual location of the colony. In 1869 Greeley sent Meeker, then employed as the agricultural editor of the Tribune, west to the Colorado Territory to seek out a location for a colony to promote settlement in the West. Meeker returned to New York City in the autumn of 1869, reporting that the South Platte Valley presented a good opportunity for the colony. In October Meeker organized the enterprise and on December 14, 1869, he placed an advertisement in the Tribune issue calling for volunteers to join him in the new venture. Meeker's advertisement specifically sought volunteers of high moral standards, who were literate and temperant. The cost of membership for those accepted to the colony was set at $155. Of the more than 3000 people who responded, Meeker selected 700 applications as prospective colonists, ninety of whom later backed out. With the collected membership fees, Meeker journeyed west again in the Spring of 1870 with two other officers. They purchased a tract of land in Weld County near the confluence of the Cache la Poudre and South Platte.
The colony thrived and expanded, attracting other homesteaders to the area. The religious nature of the colony was not agreeable to all the settlers, however, a portion of whom spread out to other nearby lands in the area (see Jacob Flowers, for example). During the 1870s the colony was particularly known for its heavy use of irrigation, with one visitor reporting that nearly every person in the cooperative was involved in the maintaining of at least one irrigation ditch. Two years later in 1872, the success of the colony inspired some of its officers to found the Fort Collins Agricultural Colony upstream on the Poudre River at Fort Collins. The city of Greeley was later incorporated in 1886. Meeker, the founder of the colony, was killed by Utes at the Meeker Massacre in western Colorado in 1879.
Although the Colony has been long dissolved, its influence is still recognized in the area and the region's history. Greeley remained a dry municipality until 1972 because of the provisions of the charter which prohibited the sale or consumption of alcohol, in accordance with the temperance requirements of the original settlers. As a result, several nearby towns grew more rapidly as the source of liquor, and at least two small towns, Rosedale, and Garden City, were established and incorporated largely to allow saloons, bars, and liquor stores to feed the demand of the University of Northern Colorado students and faculty and other residents of Greeley. Today, the City of Greeley does not provide fire protection services, which are instead provided by the Union Colony Fire Rescue Authority and the major city complex is the "Union Colony Civic Center." The irrigation system built by the Colony remains an important part of the area, although growing urbanization threatens more and more of the productive croplands the irrigation systems allowed to be utilitized.