William S. Hoofnagle, a U.S. Agriculture Department economist who in the 1960s and ’70s became a prominent civic leader in Northern Virginia, serving as chairman of the Fairfax County School Board and later the Fairfax County Board of Supervisors, died Aug. 15 at the home of a caretaker in Hayesville, N.C. He was 91.

He had cardiopulmonary arrest, said his daughter Robin Hoofnagle. Dr. Hoofnagle lived in Herndon for more than three decades before moving to Daytona Beach, Fla., in 1986 and to Hayesville in 2005.

Dr. Hoofnagle was appointed to the School Board in 1962 and served as its chairman from 1964 to 1969.

The Washington Post reported at the time that he was “widely regarded as a pivotal figure in seeing the school system . . . through its orderly desegregation in the mid-1960s.” Dr. Hoofnagle also oversaw a fast-moving expansion program for the school district, one of the largest in the area.

In January 1970, Dr. Hoofnagle took office after being appointed chairman of the Board of Supervisors. He won a special election later that year and was reelected without opposition in 1971. A Democrat at the time of his appointment, Dr. Hoofnagle served as an independent in adherence with a federal law that prohibits certain government employees from holding partisan elected office.

William S. Hoofnagle, 91, a former chairman of the Fairfax County School Board and the Fairfax County Board of Supervisors, died Aug. 15. (Bob Burchette/THE WASHINGTON POST)

In September 1972, Dr. Hoofnagle resigned from the Board of Supervisors, citing his increased work responsibilities at the Agriculture Department. He privately expressed frustration with the board chairman’s limited role, The Post reported.

In an editorial at the time, The Post described him as a “constructive mediator among his differing fellow board members” and one of the local public officials who had played “exceptional roles in coping with Greater Washington’s expansion.”

Dr. Hoofnagle retired from the Agriculture Department in 1985. During his 35-year federal career, he worked on policy related to the national school lunch program, marketing economics and international agricultural practices.

William Sherrill Hoofnagle was born in Atkins in southwestern Virginia. After Army service in Europe during World War II, he received a bachelor’s degree in education in 1947, a master’s degree in 1948 and a doctorate in rural social economics in 1951, all from the University of Virginia.

In the 1950s and ’60s, he co-founded the Herndon Realty and Insurance Agency, and the Herndon-Reston Insurance Agency. He was a past president of the Virginia School Boards Association and the Herndon Rotary Club, his daughter said.

His first wife, Shirley Goodhart Hoofnagle, died in 1979 after 32 years of marriage. Their son William B. “Ben” Hoofnagle died in 2009. A stepdaughter, Kimberley Tucker, died in 2008.

Survivors include his wife of 30 years, Janet Clayson Hoofnagle of Hayesville; two children from his first marriage, Sherrill H. Alexander of Raleigh, N.C., and Robin Hoofnagle of Arlington County; a stepdaughter, Stacey Jeuris of Fairfield, Calif.; and five grandchildren.