Agnes Fahy Johnson, a psychiatric social worker who retired several years ago from Value Options, a health-care company in Reston where she worked for nearly two decades, died Aug. 19 at Montgomery Hospice’s Casey House in Rockville. She was 78.

The cause was cancer, said her niece Margaret Sheehan McCaleb.

Mary Agnes Fahy, a Washington native, was a daughter of Charles Fahy, who served as U.S. solicitor general and later as a judge on the U.S. Court of Appeals for the D.C. Circuit.

She was a 1953 graduate of Georgetown Visitation Preparatory School and received a bachelor’s degree in sociology from what is now Trinity Washington University in 1957 and a master’s degree in social work from Catholic University in 1959.

Early in her career, she was a social worker in Wyoming and Montana and taught at the University of Montana at Missoula. She returned to the Washington area in 1982 and worked for the American Psychiatric Association before joining Value Options.

In retirement, Mrs. Johnson did volunteer work at the National Gallery of Art and the National Portrait Gallery. She was a longtime Rockville resident.

Her marriage to John C. Johnson ended in divorce. Their son, Thomas C. Johnson, died in May. Survivors include two sisters, Anne Fahy Sheehan of Bethesda and Sister Sarah Fahy, a nun with the Sisters of Notre Dame, of Washington.

— Emily Langer