Naturalization is the legal and bureaucratic process by which immigrants become United States citizens. Many immigrants simply did not go through the somewhat involved process to become citizens; Statistics of the 1830-90 censuses showed that nearly 30 percent did not become citizens. Their offspring born in the United States, however, were automatically citizens by birth. During the period of this Boone County index, various federal laws governed naturalizations. A typical example, the naturalization law of 1802 (2 Stat.153), specified that free white aliens might be admitted to citizenship provided that they:

1. declared their intention to become citizens before a competent state, territorial, or federal court of record at least 3 years before admission to citizenship;
2. took an oath of allegiance to the United States;
3. resided at least 5 years in the United States and at least 1 year in the state or territory where the court was held;
4. renounced allegiance to any foreign prince, potentate, state, or sovereignty, and;
5. satisfied the court that they were of good moral character and attached to the principles of the Constitution.

The naturalization declarations and oaths are intermixed with other subjects in the county court order books, except for a brief period in 1860 when they were kept in the Quarter Sessions Court order book (records marked with an asterisk in the table below). This listing ends somewhat arbitrarily with 1903 and may not be 100 percent complete. Later on, naturalization records were kept in the circuit court records: a Boone County circuit court naturalizations petitions book for 1908-1913 is at KDLA in Frankfort. Even later on, naturalizations became the sole responsibility of federal courts.

These records were transcribed over the years by Mrs. William A. Fitzgerald of the County Court clerk's office.