The hunt for the nearly 5 million uninsured U.S. children who are eligible for free or low-cost coverage through Medicaid or the Children’s Health Insurance Program just got a road map.

A new study published today in Health Affairs shows that 39 percent of the uninsured but eligible kids live in three states: California, Texas and Florida. Another 22 percent live in Georgia, New York, Arizona, Illinois, Ohio, Pennsylvania and North Carolina. That’s not a big surprise, because those states have more than half of all children in the country, according to the researchers at the Urban Institute, a non-partisan think tank in Washington.

The study’s real value was showing that the states with the lowest participation rates in Medicaid and CHIP were largely in the Rocky Mountain region and Florida. While the national participation rate in Medicaid/CHIP was 82 percent, five states had participation rates below 70 percent: Nevada (55.4 percent), Utah (66.2 percent), Colorado (68.9 percent), Montana (69.3 percent) and Florida (69.8 percent).

In contrast, the study showed the states with highest participation rates are Massachusetts (95 percent), Vermont (94 percent) and Maine (92 percent).

Health and Human Services Secretary Kathleen Sebelius last February challenged states, the federal government and communities to sign up the 5 million uninsured but eligible children within five years. At a press conference announcing the new study, Sebelius said the results show states have the ability to find and enroll uninsured kids.

“The study confirms that a lot of states do a very good job,” she said. “But the study also gives us a much sharper focus on where kids are who need coverage.”

Uninsured rates for children have steadily declined in recent years and are at a 20 year low, the Census Bureau reported last year. The study said a total of 7.3 million children are uninsured, but not all of them are eligible for the government programs.

Some of the poorest states had some of the highest participation rates. These included: Louisiana (88.5 percent), Arkansas (88 percent) and West Virginia (89 percent). “This shows that the highest participation rates can be achieved among a wide variety of circumstances,” said Genevieve Kenney, the lead researcher on the study and senior fellow at the Urban Institute.

States which have successfully boosted their enrollment rates have simplified or streamlined the application process, held community events and even sent people door-to-door to sign kids up.

The Obama administration plans to spend about $120 million to promote enrollment and retention in Medicaid and CHIP.

The study, which was based on 2008 data, found uninsured but eligible children in all demographic groups. However, participation rates were lower among teenagers, Hispanics and where children were living with non-U.S. citizens or with parents who did not speak English.

Surprisingly, children from the poorest households had higher participation rates in Medicaid and CHIP than those from families with more resources. The lowest participation rates were in households where the family income was at least twice the federal poverty rate, which for a family of four is $44,100.

Eligibility for Medicaid and CHIP vary by state but generally all children from families of four with incomes below $45,000 qualify. Some states go well beyond that. The programs are not available to illegal immigrants.

Neither Sebelius nor Kenney would speculate on why Nevada’s participation rate is so much lower than other states. Nevada officials could not be reached for comment because they were on furlough due to the state’s budget problems.

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