Cameron's caroling event was held Sunday evening outside The Oaks mall in Thousand Oaks.
Video of the event shows hundreds of people gathered to sing Christmas carols, few of them wearing masks or practicing social distancing.
It is generating backlash in Ventura County, which like most of Southern California is seeing a dangerous post-Thanksgiving surge in cases and hospitalizations linked to COVID-19.
Ventura County has reported nearly 27,000 COVID-19 cases since the start of the pandemic.
But on Monday alone, the county reported 2,651 new cases - a 10% increase in a single day.
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The county has reported 199 deaths from the virus and 1,307 people hospitalized since the start of the pandemic.
Cameron is best known for starring as Mike Seaver in the sitcom "Growing Pains" which ran from 1985 to 1992. In more recent years he has been active as an evangelist Christian with a ministry based in the Los Angeles area.
He and others who gathered said they wanted to celebrate their God-given liberties.
On his Instagram account, Cameron urged people to attend the event. Afterward, he said, "People had such a great time. It lifted our spirits. Over 500 people gathered."
Local officials, however, say having that many people gather in one space without masks or physical distancing is irresponsible.
"Liberty and freedom are very fragile and they come with great responsibility," said Thousand Oaks Mayor Claudia Bill-de la Pena. "Continuing to hold large gatherings and ignoring all guidelines, I feel, is unchristian."
SoCal hospital sets up refrigerated truck in case morgue runs out of space
Hospitals in Ventura County, like in most parts of Southern California, are running out of room and staffing to handle the surge in COVID-19 patients, particularly in the intensive-care units.
Available ICU capacity in the Southern California region has now dropped to a dangerously low 1.7%, state officials said Tuesday.
In the meantime, the hospital staffing situation could get worse as nurses' unions at three hospitals have voted to authorize a 10-day strike that could start Christmas Eve.
The nurses union says the possible strike at Los Robles, West Hills and Riverside hospitals is motivated in part by what they feel has been a failure by the hospital administration to protect staffers from infection during the pandemic.
Hospital administrators say they are preparing for the strike with plans to hire contract workers as they continue negotiations.