June 22, 1850: First Colorado gold found in Ralston Creek near the present location of 56th Avenue and Benton in Arvada by Lewis Ralston and his party of prospectors who continued on to California, their planned destination.
1855: Kansas Territory establishes Arapahoe County to include area of eastern Colorado to the Continental Divide.
1858: William Green Russell discovers gold near the confluence of Cherry Creek and the South Platte River, touching off the Colorado "Pikes Peak" gold rush.
November 29, 1858: The Arapahoe City Town Company organized. Although Arapahoe City existed for only a few years, it may have been the first town site in what later became Jefferson County. It was located about two miles east of Golden along Clear Creek.
1859: George A. Jackson discovers gold at present site of Idaho Springs.
June 6, 1859: Golden City established. "City" was dropped from the town's title Jan. 22, 1872.
Summer 1859: Delegates from settlements attend a constitutional convention in Denver to draft proposed state and territorial constitutions.
September 1859: Voters choose to seek establishment of a new territory rather than a new state.
October 1859: Constitutional convention adopts a provisional territorial constitution for Jefferson Territory.
November 1, 1859: The first irrigation ditch in the current Jefferson County is dug by David K. Wall, the "father of irrigated farming in Colorado." The ditch extended from Clear Creek and was used to irrigate Wall's vegetable farm. By the end of 1859 two other irrigation ditches had been dug in Jefferson County, the Wanamaker ditch off of Clear Creek and the McBroom ditch off of Bear Creek.
November 1859: Provisional Jefferson Territory territorial legislature meets and organizes twelve counties, including Jefferson County.
December 7, 1859: First newspaper, The Western Mountaineer, published in Jefferson County - April 25, 1860, by George West.
1859: Coal discovered on Coal Creek, 14 miles north of Golden.
January 2, 1860: First county election, under provisional Jefferson Territory: Golden City selected as county seat; also elected a sheriff, clerk and recorder, and county judge.
January 1860: First school in Jefferson County opened in Golden.
October 6, 1860: Birth of Charles L. Palmer, reputedly the first child of gold rush settlers to be born in Jefferson County. He served as county commissioner, 1902-1909.
1860-1862: Three mining districts formed and operated in central Jefferson County to administer extra legal law. Bergen District (Bergen Park), Junction District (Conifer), and Mt. Vernon District (Mt. Vernon Canyon) then combined under the leadership of Thomas Bergen to form short-lived Ni-Wot County.
February 28, 1861: President James Buchanan signs bill creating the Territory of Colorado.
November 1, 1861: Jefferson County one of the original 17 counties created by Colorado Territorial Legislature.
December 7, 1861: Election of county officers, including the first Board of County Commissioners.
January 6, 1862: County officials assume office.
June 20, 1862: First county tax and school tax levied by Jefferson County Commissioners.
1862-1867: Golden City is capitol of the Territory of Colorado.
1863: Henry Stevens, the first recorded homesteader in Jefferson County under the 1863 Homestead Act, builds his cabin at the current site of 44th and Teller streets in Wheat Ridge.
1864: Colorado's first railway company, the Colorado Central Railroad Company, incorporated by William A. H. Loveland in Golden.
1867: Colorado Transcript, now the Golden Transcript, the county's first enduring newspaper, founded by George West in Golden.
January 1, 1868: Golden City celebrates the ground breaking for the first railroad construction in Colorado, by the Colorado Central Railroad Company.
February 10, 1870: Colorado School of Mines established at Golden.
December 1, 1870: The first town plat of Arvada filed. Originally, the settlement was known as Ralston Point.
September 1870: The Colorado Central Railroad line from Golden to Denver completed.
1871: Town of Golden City incorporated.
October 1872: Town of Morrison established; town plat filed November 28, 1874.
December 23, 1872: The narrow gauge section of the Colorado Central Railroad, linking Denver and Golden with Central City through Clear Creek Canyon completed.
1873: Coors Brewing Company founded in Golden by Adolph Coors Sr. and Jacob Schueler. Coors bought out his partner on May 1, 1880.
1877: Dinosaur fossils discovered in Morrison Formation along the Dakota Hogback near the town of Morrison in Jefferson County; this was the first major, and one of the most important, dinosaur discoveries in North America.
1878: First county courthouse completed in Golden at 1500 Washington Avenue between present-day 15th and 16th streets.
February 12, 1881: Colorado State Industrial School for wayward boys ages 6-18, now the Lookout Mountain School for Boys, established in Golden.
1882: Unplatted area comprising Wheat Ridge named by resident Henry Lee, who served as a state senator, 1885-1889. The area was first settled as farmsteads in 1859.
April 4, 1887: Colorado State Home and Industrial School for Girls for wayward girls ages 6-18, established in Golden.
1887: Town of Broomfield established; originally called Zang's Spur, the town is located in Adams and Boulder Counties as well as Jefferson County.
May 13, 1889: Edgewater town plat filed.
July 1, 1889: Lakewood town plat filed.
1889: White Ash Coal Mine disaster. A tunnel built under Clear Creek in Golden collapsed, drowning ten men whose bodies were never recovered.
1889: First college football game played in Colorado between the Colorado School of Mines and Colorado College.
June 27, 1890: Westminster platted as Harris Park. It was originally called Harrisburg. The name was changed to Westminster in 1908.
July 19, 1890: Severe rain storm begins after a long dry spell causing Clear Creek to flood. Flood waters reach Golden at 4:00 p.m. on the 20th. The deaths of two women and an 18-month-old baby are attributed to the flood.
July 4, 1892: Mount Olivet Cemetery opened. It was called "The New City of the Dead.
1893: The first electric tramway to Lakewood and Golden from Denver completed by the Denver, Lakewood and Golden Railway Company. It later became part of the Denver Tramway Corporation and was popularly known as the "Loop."
July 27,1896: Bear Creek flood. The town of Morrison suffered the brunt of the flood.
1901: Edgewater incorporated.
August 1904: Arvada incorporated.
October 11, 1904: Town of Mountain View, or "Mount View," incorporated.
January 29, 1906: Town of Morrison incorporated.
1907: Small town of Lakeside incorporated.
1907: Death of alleged Colorado cannibal Alferd Packer, a resident of Deer Creek after his release from prison in 1901.
May 31, 1908: Lakeside Amusement Park opens.
June 1908: First automobile ascent of Castle Rock on South Table Mountain near Golden made by George Hering of Denver in his new 20-horsepower Stanley Steamer.
1908: "M" emblem for the Colorado School of Mines placed on Mount Zion by students and faculty.
1908: Thirty square mile extreme southern tip of Jefferson County transferred to Park County.
1909: Mother Frances Xavier Cabrini purchases Lookout Mountain property above Jackson Gulch on which she built a summer home for Denver orphans. The stone house was completed in 1915.
December 14, 1910: Leyden Coal Mine fire disaster, ten miners killed.
1911: Town of Westminster incorporated.
July 6, 1912: Lookout Mountain Scenic Railroad from Golden completed. The railroad was abandoned upon completion of the Lariat Trail.
April 15, 1913: Colorado Legislature passes an act authorizing the city of Denver to establish the Denver Mountain Parks in the mountain areas of Jefferson, Clear Creek, and Grand counties.
December 4, 1913: Blizzard of 1913 dumps 4 feet of snow in Golden, Arvada, and Morrison, and 5 feet in Evergreen. The death of pioneer resident John Bergen in Evergreen and the probable death of Golden dairyman John Klaassens are attributed to the storm.
1914: The Lariat Trail, also known as the Lariat Loop Road, to Lookout Mountain Park at the top of Lookout Mountain completed.
1915-1920: Tiny Town, a miniature town for children, built by George E. Turner on Turkey Creek.
June 3, 1917: Buffalo Bill buried on top of Lookout Mountain near the current site of the Pahaska Tepee
1917: Charles Boettcher's summer home on Lookout Mountain completed. The home was given to Jefferson County by Boettcher's granddaughter, Charline Breeden, in 1972; it is now open to the public for tours and special events.
April 14, 1922: The first public gathering of the Ku Klux Klan in Jefferson County on the present site of Heritage Square, complete with blazing torches. The targets of KKK intimidation in Jefferson County were Catholics, Jews, and blacks.
September 27, 1923: Ku Klux Klan burns crosses on top of South Table Mountain on Castle Rock above Golden
August 7, 1927: Dance hall on top of Golden's Castle Rock burns down.
1932: The Colorado School of Mines emblem, the "M" on Mt. Zion, lit for the first time for two nights in honor of the School of Mines homecoming events.
1936-1940: The Red Rocks Amphitheater near Morrison built by the Civilian Conservation Corps (CCC) under the Works Progress Administration (WPA) and the Denver Mountain Parks.
1941: Remington Arms Company ammunition factory established in Lakewood, now the site of the Denver Federal Center; the largest contract awarded by the federal government in Colorado up to that time.
1945: Ruth W. Quinn of Edgewater becomes the first woman to serve on a Jefferson County jury.
1947-1950: The Denver Federal Center established on the site of the Remington Arms Company facility.
1950: All 39 Jefferson County school districts consolidated into the state's largest school district, Jefferson County R-1.
1952: Jefferson County Public Library established by the Board of County Commissioners.
April 1952: Construction of Rocky Flats Atomic Energy Plant begins in Jefferson County.
November 15, 1952: The first televised Colorado college football game, Colorado School of Mines versus Colorado College, played at the School of Mines' Brooks Field and shown on KFEL-TV.
1953: New county courthouse completed in Golden at 17th and Arapahoe.
1955: Martin-Marietta Company (originally the Glen L. Martin Company), now Lockheed-Martin Company established in South Jefferson County near Waterton.
1958: Town of Bow Mar established and incorporated, located in both Jefferson and Arapahoe Counties.
1958: County jail and Sheriff's residence built next to the 1953 courthouse at 16th and Arapahoe. It was later used as the Assessor/Treasurer building.
February 9, 1960: Adolph Coors, III murdered.
October 16, 1960: Jefferson County Airport dedicated.
1961: Broomfield incorporated.
July 1963: First county courthouse on Washington Avenue demolished.
1966: Hall of Justice at 18th and Arapahoe in Golden completed.
1969: Lakewood incorporated.
1969: Wheat Ridge incorporated.
1972: Jefferson County voters approve a one-half percent sales tax for Open Space, inaugurating the county's award winning Open Space Program.
1973: Interstate-70 through Jefferson County completed.
1974: First woman, Joanne K. Patterson, elected as a county commissioner. She served 1975-1979.
1985: Detention and Sheriff's facility completed in Jefferson County Government Center at 200 Jefferson County Parkway.
May 1989: Tiny Town reopens after restoration.
1989: Human Services building completed in Jefferson County Government Center campus at 900 Jefferson County Parkway.
1990: C-470 highway completed through Jefferson County.
1993: Administration and Courts facility completed in Jefferson County Government Center at 100 Jefferson County Parkway.
1995: Old 1953 Courthouse, Hall of Justice, and Assessor/Treasurer building sold to Colorado School of Mines.
1997: District Attorney building completed in Jefferson County Government Center at 500 Jefferson County Parkway.
September 1997: Seventeen-member Russian delegation from Jefferson County's sister county, Tver Oblast, visits Jefferson County and other areas in the state.
November 24-26, 1999: Old 1953 Courthouse demolished by Colorado School of Mines.
November 15, 2001: The city of four counties (Boulder, Adams, Weld, and Jefferson) officially becomes the City and County of Broomfield.
Compiled by Jefferson County Records Management & Archives.