Officials at the center say Betty Ford approved the donation in mid-June, three weeks before she died on July 8.
"Mrs. Ford was and always will be the heart and soul of this place of healing," Mary Pattiz, chairman of the Betty Ford Center Board of Directors. "It means so much to us that after all she had given over the past 30 years, the center was still front and center in her mind during her final days."
The $400,000 donation was authorized in her will. The center will get an additional $100,000 from a foundation set up by former President Gerald Ford and his wife 10 years ago.
The Betty Ford Center, located in Rancho Mirage, was co-founded by Betty Ford in 1982. It has treated nearly 100,000 patients, including numerous Hollywood celebrities, for drug and alcohol dependency.
The Associated Press contributed to this report.