The following important events in the history of Colorado affected political boundaries, record keeping, and family movements.
- 1706: Claimed for Spain by Juan de Ulibarri
- 1803: The United States acquired the sections of Colorado north and east of the Arkansas River as part of the Louisiana Purchase. Beginning in 1806 government expeditions were sent to map the area, and fur trappers and traders followed in the
- 1806: Explored by Zebulon Pike.
- 1820's Western settlers in the 1840s and 1850s bypassed Colorado on their way to the Pacific Coast.
- 1842: Explored by John C. Freemont.
- 1845: Central part of Colorado acquired with the admission of Texas as a state.
- 1848: The United States acquired the rest of present-day Colorado from Mexico.
- 1851: Hispanic families from New Mexico founded San Luis, the oldest continually occupied town in Colorado.
- 1854: The Colorado area was divided politically among the territories of Kansas, Nebraska, Utah, and New Mexico.
- 1858: Denver and other mining towns were organized by Colorado's early gold seekers. In 1858 the miners also organized Arapahoe County of Kansas Territory.
- 1859: Colorado pioneers created what they called Jefferson Territory without the sanction of Congress. It was to have included all of present-day Colorado and some areas of Utah and Wyoming.
- 1861: Arapaho and Cheyenne Indians ceded land.
- 1861: (February 28,) Congress organized the Colorado Territory. The first seventeen counties were organized the same year.
- 1864: (November 29,) Col. John M. Chivington and troops attacked the Cheyenne Indians camped on Sand Creek 150 Indians were killed.
- 1865: Arapaho, Cheyenne, Comanche and Kiowa Indians ceded land.
- 1867-1869: Indian Champaign
- 1868: Shoshone and Ute Indians ceded land.
- 1870: Many Indians removed to Oklahoma.
- 1870: Railroad links between Denver and Cheyenne and between Denver and Kansas City connected Colorado with the east and west coasts.
- 1874: Ute Indians ceded land.
- 1874-1875: Indian Campaign
- 1876: (August 1,) Colorado became a state.
- 1878-1879: Northern Cheyenne Indians, lead by Chief Dull Knife, Wild Hog and Little Wolf surrendered in Colorado to U.S. forces. They were sent to Ft. Reno, Oklahoma, Later settled on a reservation in Montana.
- 1879: (Summer) White River Ute Indians staged an armed uprising. A treaty was signed and the entire nation was removed to a reservation in Utah.
- 1880: (western Colorado) Ute Indians ceded land and were removed to Utah.
- 1881: Western Colorado was officially opened to white settlement after most of the Ute Indians had been moved to reservations in Utah.
- 1890: Colorado's population exceeded 400,000 when the last major gold strike was made at Cripple Creek.
- 1898: Over 300,000 men were involved in the Spanish-American War which was fought mainly in Cuba and the Philippines.
- 1917–1918: More than 26 million men from the United States ages 18 through 45 registered with the Selective Service. World War I over 4.7 million American men and women served during the war.
- 1930's: The Great Depression closed many factories and mills. Many small farms were abandoned, and many families moved to cities.
- 1940–1945: Over 50.6 million men ages 18 to 65 registered with the Selective Service. Over 16.3 million American men and women served in the armed forces during World War II.
- 1950–1953: Over 5.7 million American men and women served in the Korean War.
- 1950's–1960's The building of interstate highways made it easier for people to move long distances.
- 1964–1972: Over 8.7 million American men and women served in the Vietnam War.
Histories are great sources of genealogical information. Many contain biographical information about individuals who lived in the area, including:
Some of the most valuable sources for family history research are local histories. Published histories of towns, counties, and states usually contain accounts of families. They describe the settlement of the area and the founding of churches, schools, and businesses. You can also find lists of pioneers, soldiers, and civil officials. Even if your ancestor is not listed, information on other relatives may be included that will provide important clues for locating your ancestor. A local history may also suggest other records to search. Local histories are extensively collected by the Family History Library, public and university libraries, and state and local historical societies.
State Histories Useful to Genealogists
Good genealogists strive to understand the life and times of their ancestors. In this sense, any history is useful. But certain kinds of state, county, and local histories, especially older histories published between 1845 and 1945, often include biographical sketches of prominent individuals. The sketches usually tend toward the laudatory, but may include some genealogical details. If these histories are indexed or alphabetical, check for an ancestor's name. Some examples for the State of Colorado are:
An especially helpful source for studying the history of Colorado is Colorado and Its People: A Narrative and Topical History of the Centennial State  Volumes 3-4 contain personal and family histories.
- A bibliography of local histories is found in Colorado Bibliography 
United States History
The following are only a few of the many sources that are available at most large libraries:
- The Almanac of American History, This provides brief historical essays and chronological descriptions of thousands of key events in United States history.
- Webster's Guide to American History: A Chronological, Geographical, and Biographical Survey and Compendium  This includes a history, some maps, tables, and other historical information.
- Dictionary of American History, Revised ed  This includes historical sketches on various topics in U.S. history, such as wars, people, laws, and organizations.
To find more books and articles about Colorado's history use the Internet Google search for phases like "Colorado history." Family History Library Catalog Surname Search lists many more histories under topics like:
- COLORADO- HISTORY
- COLORADO, [COUNTY] - HISTORY
- COLORADO, [COUNTY], [TOWN] - HISTORY
- COLORADO, BIBLIOGRAPHY
- Filby, P. William. A Bibliography of American County Histories. Baltimore: Genealogical Publishing, 1985. (FHL book 973 H23bi)
- Kaminkow, Marion J. United States Local Histories in the Library of Congress. 5 vols. Baltimore: Magna Charta Book, 1975-76. (FHL book 973 A3ka.)
- LeRoy R. Hafen, ed., Colorado and Its People: A Narrative and Topical History of the Centennial State, Four Volumes. (New York, NY: Lewis Historical Publishing Co., 1948; Family History Library book 978.8 H2h; film 1000143).
- Bohdan S. Wynar and Roberta J. Depp, eds., Colorado Bibliography (Littleton, Colorado: Libraries Unlimited, 1980; Family History Library book 978.8 A3c, pages 53-92).
- Schlesinger, Jr., Arthur M. The Almanac of American History. Greenwich, Conn.: Bison Books, 1983. (FHL book 973 H2alm)
- Webster's Guide to American History: A Chronological, Geographical, and Biographical Survey and Compendium. Springfield, Mass.: G&C Merriam, 1971. (FHL book 973 H2v)
- Dictionary of American History, Revised ed., 8 vols. New York: Charles Scribner's Sons, 1976. (FHL book 973 H2ad.)