Since 1968 our goal has been straightforward: help clients get their life back on track and achieve a life of sobriety, free from drug use and symptoms of mental illness. A life that is productive, socially responsible, and healthy. Gateway Foundation is the largest nonprofit treatment provider with treatment programs in California, Delaware, Florida, Illinois, Michigan, Missouri, New Jersey, Texas and Wyoming that specialize in substance use disorders for men, women, adolescents, and clients diagnosed with co-occurring mental health disorders.