Former San Mateo County Sheriff and County Supervisor Don Horsley has died at age 80, the sheriff's office confirmed Friday evening.

The San Mateo County Sheriff's said in an Instagram post that Horsley died on the morning of Friday, Nov. 24.

"This is a very sad day for San Mateo County," said state Assemblyman Marc Berman, D-Menlo Park, in a post on X. "Don Horsley was a remarkable man and a tireless public servant who always focused on helping the underserved. He was always there with advice (spend more time on the Coastside!), but was never pushy. I’m going to miss him."

An obituary posted on the San Mateo County website characterized Horsley as "a former teacher and beat cop whose bold ideas for reforms propelled him" to two of the top elected positions in the county.

Horsley started at the San Mateo County Sheriff’s Office in 1972, initially serving as a patrol deputy in East Palo Alto. In 1993, Horsley was elected as county sheriff, a position he held for more than a decade. He retired in 2007.

During his time in the Sheriff's Office, Horsley spent extensive time upgrading the training of deputy sheriffs and correctional officers, and played a key role in planning for a new correctional center, including mental and medical health care facilities, according to the county's obituary.

“I ran for San Mateo County Sheriff in 1993 because I saw the need for innovative leadership, modernization and upgrading the tools for law enforcement officers,” Horsley was quoted as saying.

In 2006, Horsley was elected to the board of Sequoia Healthcare District, after running to unseat contrarian board member Jack Hickey, a longtime critic who vowed to dissolve the district.

At age 66, he won a seat on the San Mateo County Board of Supervisors in 2010. After being reelected twice, term limits prevented him from running again in 2022.

"Don’s life was dedicated to public service. His tremendous legacy and impact will not be forgotten," said Supervisor Ray Mueller in a post on X. Mueller was elected to Horsley's District 3 seat in 2022. District 3 represents Atherton, Half Moon Bay, Pacifica, Portola Valley, Woodside and part of Belmont, along with large unincorporated areas.

State Sen. Josh Becker, D-Menlo Park, called Horsley a "pioneering figure in San Mateo County" in a post on X and remembered him as a devoted public servant who improved the lives of many people in the community he served.

“Don was a class act and a man who cared a great deal about the most vulnerable in our community,” said County Executive Mike Callagy in a statement.

“Don was a caring man with a great sense of humor, and he lived a full and distinguished life. He made a great difference in this county and his legacy will live on through all of the great projects and work that he was involved in,” he said.

Horsley traced his concern for the treatment of the mentally ill to his boyhood, when his grandmother was confined to a mental health hospital, according to the county's obituary.

“It was all concrete and slamming doors,” Mr. Horsley recounted in April 2021 at the groundbreaking for a new mental health center he championed. “Because of that, being a little boy, seeing a state hospital and women who are essentially locked up in a concrete monstrosity, I guess touched something inside me such that I was always interested in doing better for people who have mental health issues.”

Born in San Francisco, Horsley moved with his family to Daly City, where he attended Westmoor High School, according to the statement released by the county. He earned a bachelor’s degree from San Francisco State University, worked for the Daly City Police Department, then became a juvenile counselor for the San Mateo County Probation Department and a middle school teacher.

When he returned to a career in law enforcement, his first stop was the Pacifica Police Department before joining the San Mateo County Sheriff’s Office in 1972 as a deputy.

According to the sheriff’s office, Horsley began the Sheriff’s Activity League (SAL) in 1997. The SAL program is focused on improving interactions between law enforcement and youth.

In an article on Horsley’s retirement from the Board of Supervisors, former County Manager John Maltbie said, “Don represents what good government is all about, a caring individual wanting to serve his community."

Information on services and survivors was not immediately available.

Almanac Senior Editor Andrea Gemmet contributed to this report.