"We are saddened to announce the passing of one of our own RSO family members, Deputy Terrell Young," the department said in a statement.
Young, a 15-year veteran of the department, was its first to succumb to COVID-19, the statement said. He is survived by his wife and four children.
The deputy's body was transported to Murrieta Valley Funeral home in a hearse that was escorted by a procession of dozens of motorcycle officers.
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According to the Riverside Sheriff's Association, Young began his career with the department in December 2005. He worked assignments at the Larry Smith Correctional Facility, Perris Station, Court Services, Southwest Station and the Cois Byrd Detention Center.
"Our association family, and law enforcement family as a whole, mourns the community the tragic death of Deputy Young," Bill Young, president of the organization, said. "We continue to urge everyone that this virus is real, it is deadly, and we should continue to maintain social-distancing as much as possible."
Law enforcement and health officials took to social media to express their sympathies.
"Sending my sincere condolences to Deputy Young's loved ones and to our friends and partners at @RSO," Kim Saruwatari," director for Riverside University Health System-Public Health, said on Twitter. "Such a tragic loss. #rivconow"
"Please accept my deepest condolences on behalf of our #LASD family," Los Angeles County Sheriff Alex Villanueva tweeted. "We grieve alongside you. We are enduring this together and are here for you, if you need us."
At a Thursday evening press conference, Sheriff Chad Bianco said Young transported a coronavirus-positive inmate on March 16 and started showing symptoms on March 22 and went home. Ten other deputies also called in sick with symptoms that day, Bianco said.
Twenty-five employees of the department have tested positive for COVID-19, 22 of which work at the Cois Byrd Detention Center, while 16 others are still awaiting test results, according to Bianco. Several coronavirus-positive employees are still in the hospital, including one in critical condition.
Out of more than 100 inmates who have been tested, eleven inmates in Riverside County jails were confirmed to have contracted the virus. The public is being asked to void the jails. Visits will no longer be allowed unless it involves legitimate business, such as attorneys.
Bianco added that the entire department is still coming to terms with Young's death, which he described as "a lot different than any on-duty death we've ever experienced."
"If you want to honor his death, stay home. Quit going to work. As long as this virus continues to spread, it's not going to end," he said.