Colorado Naturalization and Citizenship
Naturalization records were filed in local or federal courts until 1906 when the U.S. district courts were given jurisdiction. Some territorial and early statehood records are at the Colorado Division of Archives and Public Records. The National Archives and Records Administration—Rocky Mountain Region has declarations and petitions for the years 1877 to 1952 for the U.S. District Courts of Denver, Pueblo, Del Norte, and Montrose. The U.S. District Court in Denver has an index to naturalizations granted in these courts since 1876.
The Family History Library has microfilms of U.S. District Courts Naturalization Records for Denver (1877-1952) and Pueblo for the years (1906-1949).
The Colorado Genealogical Society has indexed abstracts of some naturalization records and published these in The Colorado Genealogist (see the "Periodicals" section).
For naturalization records after September 1906, contact the National Archives—Rocky Mountain Region or the local office of the Immigration and Naturalization Service, or order films from the Family History Library.