Naturalizations for Union County, Indiana may be found in:

• Court Order Books (See Union County Court Records)
• Probate Order Books (See Union County Probate Records)
• Separate naturalization volumes

Online:

• Union County Naturalizations, 1860-1939

FHL Microfilm

• Naturalizations, 1860-1939

Books:

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