When federal lawmakers wrote the act overhauling the nation’s health-care system six years ago, they ruled out any possibility of extending health insurance to illegal immigrants.

Local officials where many of those immigrants live are treating them anyway.

A Wall Street Journal survey of the 25 U.S. counties with the largest unauthorized immigrant populations found that 20 of them have programs that pay for the low-income uninsured to have doctor visits, shots, prescription drugs, lab tests and surgeries at local providers. The services usually are inexpensive or free to participants, who must prove they live in the county but are told their immigration status doesn’t matter.

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