Should be resident address. In addition, Illinois and Indiana are neighbor. N-400 forms applicants from Illinois and Indiana share same USCIS filing address.
LINK: http://www.uscis.gov/n-400
If you reside in Alaska, Arizona, California, Colorado, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, North Dakota, Ohio, Oregon, South Dakota, Utah, Washington, Wisconsin, Wyoming, Territory of Guam, or the Commonwealth of the Northern Mariana Islands, send your application to the USCIS Phoenix Lockbox Facility at the following address:
USCIS
P.O. Box 21251
Phoenix, AZ 85036
For Express Mail or courier deliveries, use the following address:
USCIS
Attn: N-400
1820 E. Skyharbor Circle S
Suite 100
Phoenix, AZ 85034