Fairfax County Supervisor Catherine M. Hudgins (D-Hunter Mills) was elected in 1999. (Evan Cantwell)

Fairfax County Supervisor Catherine M. Hudgins announced Tuesday that she will not seek reelection in November, adding to a political transformation underway in Virginia’s largest jurisdiction, where five board seats will now come open at the end of this year.

Hudgins, 74, made her announcement during a county board meeting, saying simply that she will step down at the end of what will be her 20th year as the Democratic supervisor representing the Hunter Mill district.

While expected, Hudgins’s announcement underscores the dramatic changes facing Fairfax County’s 10-member Board of Supervisors.

Board chairman Sharon ­Bulova (D) and Supervisors Linda Q. Smyth (D-Providence) and John C. Cook (R-Braddock) have also announced that they will step down. Supervisor Jeff C. McKay (D-Lee) is seeking to replace Bulova, leaving his district seat open.

Hudgins was elected in 1999 as Fairfax County’s first African American supervisor, joining the board after serving as chief of staff to then-Chairman Katherine Hanley.

A former consultant to the AT&T telecommunications company who previously worked as a math teacher, Hudgins maintained a quiet, studied presence on the board.

She has been instrumental in the steady transformation of the Reston area, which now includes high-rise apartment buildings and office towers near Metro’s Silver Line, and she has drawn criticism from residents frustrated by increased traffic and crowded classrooms.

In 2017, Hudgins also helped push through a One Fairfax ­policy that uses social and racial equity as guidelines for county spending and land-use decisions.

Recently, Hudgins was diagnosed with breast cancer. That diagnosis, and the 2015 death of her husband, Willie L. Hudgins, prompted speculation that she would soon retire.

In anticipation of her decision, three Democrats — attorney Laurie Tyler Dodd, small-business owner Shyamali Hauth and Parker Messick, a recent Roanoke College graduate — had already announced they would seek the seat.

In the board chambers Tuesday, Hudgins’s announcement drew some emotional reactions from her colleagues. Bulova, reflecting on her own pending retirement, remarked that it can be difficult to deliver such news.

“Yes, it is,” Hudgins quietly replied.