The following important events in the history of Montana affected political boundaries, record keeping, and family movements.
- 1803-1850s: The United States acquired from France the area of Montana east of the mountains. Britain relinquished its claims to the western section in 1846. Until the 1850s, Montana was the domain of Indians, explorers, fur traders, trappers, and missionaries.
- 1841: Jesuit priests founded St. Mary's mission. In the 1850's this mission became the center of ranching activity in the Bitterroot Valley of western Montana.
- 1846: Fort Benton, the only Montana trading post to become a permanent settlement, was established on the Missouri River.
- 1855:(July 16,) Through the Treaty of Hell Gate the Salish and Kutenai (Kootnai) Indians ceded their lands to the United States.
- 1859: Steamboats first reached Fort Benton.
- 1860s: Montana west of the continental divide was designated Missoula County, Washington Territory, in 1860. In 1861 the unsettled eastern portion was attached to Dakota Territory. In 1863 and 1864 all of Montana was included in Idaho Territory.
- 1862-1864: The discovery of gold in western Montana brought an influx of miners to Bannack, Virginia City, and Helena. Many of the miners began farming and set up supply centers—such as Missoula, Deer Lodge, and Bozeman.
- 1864: Montana Territory was established with nine counties.(March 26,)
- 1870: (January 22,) Piegan Indian village was attacked by troops of the U.S. Cavalry under cammand of Col. E. M. Baker, 174 Indians killed, 140 taken prisoner.
- 1867-1877 Indian Wars
- 1876 (June 25,) Sioux Wars General George Armstrong Custer and 265 men of the 7th Cavalry slaughtered by Cheyenne and Sioux Indians at the Battle of Little Big Horn.
- 1879 Cheyenne
- 1880s: Railroads first crossed Montana. The population of the territory was about 40,000.
- 1889: Montana became a state. (November 8,)
- 1892 (October 15,) Crow Indian reservation opened to settlers by Presidential proclamation. The territory covered 1,800,000 acres.
- 1898: Over 300,000 men were involved in the Spanish-American War which was fought mainly in Cuba and the Philippines.
- 1910-1925: The number of counties doubled from 28 to the present 56 as homesteaders moved into eastern Montana. By 1930 a cycle of drought years had driven many of the settlers from the state
- 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. The United States Research "History" page cites nationwide bibliographies of local histories which include histories of Montana.
- Montana's Genealogical and Local History Records has local histories listed for Montana's counties. 
- A History of Montana is an especially helpful source for studying the history of Montana and has family histories
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 Montana are:
United States History
The following are only a few of the many sources that are available:
- The Almanac of American History,   This provides brief historical essays and chronological descriptions of thousands of key events in United States history.
- Dictionary of American History, Revised ed   This includes historical sketches on various topics in U.S. history, such as wars, people, laws, and organizations. A snippet view is available at Google books.
- 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.
To find more books and articles about Montana 's history use the Internet Google search for phases like "Montana history." Family History Library Catalog Surname Search lists many more histories under topics like:
- MONTANA- HISTORY
- MONTANA, [COUNTY] - HISTORY
- MONTANA, [COUNTY], [TOWN] - HISTORY
- MONTANA, BIBLIOGRAPHY
- Dennis Lee Richards' Montana's Genealogical and Local History Records... Detroit: Gale Research Company, 1981. (FHL 978.6 A3r; fiche 6019973.)
- Merrill G. Burlingame and K. Ross Toole, Editors, A History of Montana, Three Volumes. (New York, NY: Lewis Historical Publishing Company, 1957; Family History Library book 978.6 H2b). Volume 3
- 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.)
- Schlesinger, Jr., Arthur M. The Almanac of American History. Greenwich, Conn.: Bison Books, 1983. (FHL book 973 H2alm)
- Dictionary of American History, Revised ed., 8 vols. New York: Charles Scribner's Sons, 1976. (FHL book 973 H2ad.)
- Webster's Guide to American History: A Chronological, Geographical, and Biographical Survey and Compendium. Springfield, Mass.: G&C Merriam, 1971. (FHL book 973 H2v)
- Limited view at Google Books
- Writings on American History By American Historical Association, Library of Congress, United States National Historical Publications Commission, Published by KTO Press, 1921 FHL book 973 H23w