How do I join? Last Modified Monday July 06, 2015 Joining Alliant is easy. You can complete our secure online membership application. Alternatively, you can download and mail in your completed member enrollment application (PDF) to: U.S Postal Service Delivery Overnight Service Alliant Credit Union Alliant Credit Union Attn. Account Services Attn. Account Services P.O. Box 66945 11545 W. Touhy Ave. Chicago, IL 60666-0945 Chicago, IL 60666 Note: If you have a credit freeze, please temporarily release it in order to apply. If you are opening an account for a minor or have a Fraud Victim Alert with a credit bureau, you will have to mail us a member enrollment application (PDF). For more information, please contact us anytime at (800) 328-1935 (24/7).