- Abbott
- Abraham Lincoln Memorial Hospital
- ACT Expocad
- Ad+one
- Advance Clinical Resources
- Advantage Chevrolet
- Advocate BroMenn Medical Center
- Advocate Children's Hospital
- Advocate Christ Medical Center
- Advocate Condell Medical Center
- Advocate Eureka Hospital
- Advocate Good Samaritan Hospital
- Advocate Good Shepherd Hospital
- Advocate Health Lutheran General
- Advocate Illinois Masonic Medical Center
- Advocate Lutheran General Hospital
- Advocate Sherman Hospital
- Advocate South Suburban Hospital
- Advocate Trinity Hospital
- Alenza
- Alexian Brothers Medical Center
- ALL Masonry Construction Company Inc.
- Aluminum Anodizers Council
- Alzheimer's Association
- American Academy of Cosmetic Surgery
- American Academy of Dermatology
- American Academy of Dermatology
- American Academy of Medical Administrators
- American Academy of Orthopaedic Surgeons
- American Academy of Pediatrics
- American College of Chest Physicians
- American College of Healthcare Executives
- American College of Osteopathic Family Physicians
- American Dental Association
- American Dietetic Association
- American Express Tax and Business Services of Illinois
- American Health Information Management Association
- American Hospital Association
- American Legion - Department of Illinois
- American Medical Association
- American Osteopathic Association
- American Society For Clinical Pathology
- American Society for Quality, Section 1205
- American Society for Surgery of the Hand
- American Society of Safety Professionals
- AMITA Health Adventist Hospital Hinsdale
- AMITA Health Adventist Medical Center Bolingbrook
- AMITA Health Adventist Medical Center GlenOaks
- AMITA Health Adventist Medical Center La Grange
- AMITA Health Mercy Medical Center Aurora