We inform a county's efforts to provide health insurance to uninsured working immigrants-a group left out of national and state strategies that aim to expand coverage. We analyzed a population-based survey data administered in English, Spanish, Cantonese, Mandarin, Korean, Vietnamese, and Dari on 5,540 nonelderly adult workers in Alameda County, California. The study models the likelihood of employment-based coverage, estimates the eligibility for public programs, and evaluates the affordability of average employee share of premiums by citizenship status and years lived in the United States (tenure). Immigrant workers in Alameda County are disproportionately uninsured. They constitute 29% of the employee labor force but 54% of uninsured employees. Employment-based coverage increased with citizenship and length of stay (tenure) in the United States. Noncitizens with less than 5 years residency in the United States faced the greatest disadvantage in securing employment-based coverage, an effect that is greater than disadvantages associated with race/ethnicity. A citizenship-tenure divide existed in obtaining employment-based coverage, suggesting that policies focusing on noncitizen and new immigrant workers would greatly relieve the disparate uninsured rates among workers. The expansion of nonemployment-based coverage programs would cover more than 30% of Alameda County's uninsured immigrant workers; but subsidies will also be needed for the lowest-income workers who are not eligible for these programs.