Longmont, Colorado  Longmont is a Home Rule Municipality in Boulder and Weld counties of the U.S. state of Colorado. Longmont is located northeast of the county seat of Boulder and north-northwest of the Colorado State Capitol in Denver. Longmont's population was 86,270 at the time of the 2010 U.S. Census. Longmont is the 13th most populous city in the state of Colorado. The word "Longmont" comes from Longs Peak, a prominent mountain named for explorer Stephen H. Long that is clearly visible from Longmont, and "mont", from the French word "montagne" for mountain. Longmont was founded in 1871 by a group of people from Chicago, Illinois. Originally called the Chicago-Colorado Colony, the men sold memberships in the town and with the proceeds purchased the land necessary for the town hall. As the first planned community in Boulder County, the city streets were laid out in a grid plan in a square mile. The city began to flourish as an agricultural community after the building of the Colorado Central Railroad line arrived northward from Boulder in 1877. During the 1940s, Longmont began to grow beyond these original limits. In 1925, the Ku Klux Klan gained control of Longmont 's City Council in an election. They began construction of a large pork-barrel project, Chimney Rock Dam, above Lyons and marched up and down Main Street in their costumes. In the 1927 election they were voted out of office, and their influence soon declined. Work on Chimney Rock Dam was abandoned as unfeasible, and its foundations are still visible in the St. Vrain River. During the 1960s the federal government built an air route traffic control center in Longmont, and IBM built a manufacturing and development campus near Longmont. As agriculture waned, more high technology has come to the city, including companies like Seagate and Amgen; Amgen closed its Longmont campus in 2015. In April 2009, the GE Energy Company relocated its control solutions business to the area. The downtown along Main Street, once nearly dead during the 1980s, has seen a vibrant revival in the 1990s and into the 21st century. During the mid-1990s, the southern edge of Longmont became the location of the first New Urbanist project in Colorado, called Prospect New Town, designed by the architects Andrés Duany and Elizabeth Plater-Zyberk. Longmont was the site of Colorado's first library though it didn't last more than a year before its collection of 300 books was lost.