Dearborn County, Indiana naturalizations were recorded in:

• Court Order Books
• Probate Order Books
• Separate naturalization volumes

Online databases:

• Dearborn County Naturalization Books, 1838-1905
• Dearborn County Naturalizations from Court Records, 1826-1849

Microfilm:

• Indiana State Library (1838-1890)
• Family History Library (1838-1905)

Books:

• An Index to Naturalization Records in Pre-1907 Indiana County Courts. Indiana Historical Society : Indianapolis, 2001. [Amazon Affiliate Link]