A new requirement that masks be worn indoors in Los Angeles County went into effect at midnight on Saturday night. But the local sheriff has no plans to enforce it.

“Forcing the vaccinated and those who already contracted Covid-19 to wear masks indoors is not backed by science,” Sheriff Alex Villanueva wrote in a statement posted on his department’s website on Friday.

The department “will not expend our limited resources and instead ask for voluntary compliance,” the statement continued.

County public health officials had been urging residents for weeks to wear masks indoors as the highly contagious Delta variant spread in the state, as it is doing across the country.

But with California fully reopened and pandemic restrictions lifted, it remains unclear how willing the public will be to pick up their masks again — especially with little enforcement.

The Los Angeles County Department of Public Health could issue a notice of violation or a citation to businesses that fail to comply with the mandate, a spokeswoman, Natalie Jimenez, wrote in an email on Saturday. But she said that “education and information sharing” would be the department’s primary approaches.

“Our community will not be able to enforce our way out of this pandemic; we need everyone doing their part to keep themselves and each other safe,” Ms. Jimenez wrote.

Enforcing mask mandates proved an enduring challenge for public health officials across the country in earlier phases of the pandemic, as concerns about the virus’s spread, crushing hospital loads and a staggering national death toll clashed with politicized outcries over threats to personal liberty and rampant misinformation.

In Los Angeles County, Sheriff Villanueva repeatedly declined to enforce Covid restrictions, including a statewide stay-at-home order last winter. Last summer, the county’s inspector general warned that sheriff’s deputies weren’t following orders requiring them to wear masks on the job.

The Los Angeles County mask requirement was reintroduced because the Delta-driven surge presents risks that earlier versions of the virus did not, according to the county health department.

“People with only one vaccine are not as well protected, and there is evidence that a very small number of fully vaccinated individuals can become infected and may be able to infect others,” said a statement the department issued on Thursday.

Masks will continue to be required in public schools statewide, though the Centers for Disease Control and Prevention recommended that masks be optional for fully vaccinated students and staff members.

L.A. County is averaging almost 1,400 new cases a day, a 251 percent increase from the average two weeks ago, and Covid hospitalizations are up 27 percent, according to a New York Times database. Still, the current situation is far less grave for the county than during the peak over the winter, when new cases hit an average of over 16,000 and hospitalizations rose to an average of more than 7,000.

Daily deaths have also remained in the single digits, down from winter’s average high of more than 240.