Missouri Naturalization and Citizenship
Naturalization records have been filed primarily in the circuit courts. In earlier years naturalization information was included in the minutes and order books of various courts along with other court matters. Eventually the papers were kept in separate volumes with indexes. You may obtain copies of declarations, petitions, and certificates by contacting the clerk's office in each county courthouse.
The Family History Library has copies of the records for some counties in the state. For St. Louis, for example, the library has 17 microfilms of an index to naturalizations from the Circuit Court for 1840 to 1906.
After 1906, most records are under the jurisdiction of a U.S. district court. If you need naturalization records after that date, contact a federal office of the Immigration and Naturalization Service or the National Archives—Central Plains Region (Kansas City). The Archives maintains records from the U.S. Eastern District Court, 1907 to 1941, and the Western District Court, 1906 to 1924.