As the holidays approached, Dr. Christina Gomez-Mira was helping one of her undocumented patients get the right medication for her arthritis. The 42-year-old woman had been uninsured since she came to America. Over Christmas, she ran out of her anti-inflammatory medication. 

This week, Ms. Gomez-Mira’s patient signed up for Medi-Cal, which became available to undocumented immigrants aged 26 to 49 on Jan. 1. The state’s health insurance program for those with very low incomes had covered undocumented immigrants of other age groups, but this year’s expansion closed the last gap. 

California is the only state to fund comprehensive health care for undocumented immigrants, who make up an estimated 9 percent of the state’s workforce. The change is a huge step toward covering vulnerable populations in West Marin, where 15 percent of patients at the Petaluma Health Center’s Point Reyes Health Clinic are uninsured. According to Pedro Toledo, the center’s chief administrative officer, about a quarter of the center’s uninsured clients are now eligible for Medi-Cal.

Mr. Toledo said the expansion will help destigmatize health care and provide insights into undocumented population numbers. The center’s Covid vaccination outreach identified 4,870 undocumented, low-income workers who were not already patients in West Marin and Petaluma, most of whom worked multiple jobs. 

“What we learned in the pandemic is that there are a lot of essential workers that have never come into care through the health center or hospitals,” Mr. Toledo said. “They were mostly younger men working in farms, restaurants or grocery stores. Men are the least likely to come into care. Women tend to come into care a lot more because they have more family planning and checkups. Part of it is, even if you’re coming to a community health center, there’s a fee—the lowest is about $20. That buys lunch.”

In 2022, the Point Reyes Health Clinic had 3,000 patients on Medi-Cal, according to Chloe Cook, who manages West Marin Health and Human Services. She called the expansion a step in the right direction toward providing coverage for essential workers in the community. 

“Our tourist industry is run by people at different stages of documentation,” Ms. Cook said. “They’re not just farm or ranch workers, they’re providing elder care and childcare, and without them, West Marin could not run. The rising tide floats all boats.”

Medi-Cal, the state’s version of the federal Medicaid program, offers free or low-cost health insurance for California residents whose income is 138 percent or less of the national poverty level. In 2023, Medi-Cal’s maximum income level for an individual was $20,100, or $27,200 for a two-person family. Medi-Cal has no premiums, co-payments or out-of-pocket costs. 

In 2015, then-Governor Jerry Brown signed legislation allowing undocumented children to enroll in Medi-Cal. Four years later, Gov. Gavin Newsom expanded access to young adults aged 19 through 25. In 2022, adults aged 50 and older were included.

According to the University of California, Los Angeles Latino Policy and Politics Institute, the latest expansion will impact the largest number of immigrants yet—as many as 700,000. 

Most of Marin’s undocumented immigrants live in District Four, either in San Rafael’s Canal District or West Marin, said Fernando Barreto, an aide to Supervisor Dennis Rodoni. He said the number of undocumented immigrants in Marin is between 12,000 and 15,000, or up to 6 percent of the population. 

Mr. Barreto called the Medi-Cal expansion a win-win. Eliminating concerns related to immigration status is among the first steps in bridging a segregated community like Marin, he said. “Undocumented immigrants in Marin County, like those across California, have historically faced barriers in accessing health care due to their immigration status, and this expansion of Medi-Cal coverage can be transformative,” he said.

According to Ms. Cook, some in the undocumented community fear that signing up with Medi-Cal could subject them to qualify as a “public charge,” an element of immigration law that can disqualify someone from gaining citizenship for depending too heavily on the U.S. government. Yet the Department of Homeland Security and U.S. Citizenship and Immigration Services do not consider receipt of health, food, and housing benefits as part of a public charge determination.

At West Marin Health and Human Services, Ms. Cook is pushing for broader access to health care, and her office helps Spanish-speaking people apply for services and benefits. Of the clients who use that service, 73 percent are age 30 to 50. 

But there’s still a strong divide in who’s seeking that care. Across all ethnic groups, men access health care less than women do. A 2019 study by U.C.L.A. found that the gender gap for uninsured Latinos was greater than for uninsured whites.