WASHINGTON (AP) -- Wanted: Millions of uninsured Americans willing to give President Barack Obama's health care law a chance.
With time running out, it may not be so hard for the administration and its allies to find them. A study for The Associated Press finds that the uninsured aren't scattered evenly across the country: half of them live in just 116 of the nation's 3,143 counties.
That means outreach targeted to select areas can pay off big, reaching millions of prospective customers needed to stabilize the law's new insurance markets.
The pattern also holds true for the younger uninsured, the health care overhaul's most coveted demographic. The study found that half of uninsured people ages 19-39 live in 108 counties. Their premiums are needed to offset the cost of care for older adults.
With most of the bugs out of the HealthCare.gov website, the Obama administration is using the geography of the uninsured to write a playbook for its closing sign-up campaign.
Enrollment ends March 31 for subsidized private insurance, available to people who don't have coverage at work. But many who could benefit are procrastinating. Some people are confused by the new law. Others don't think they will qualify for help.
"Our efforts are aimed at making sure we can raise awareness in areas with the largest concentration of uninsured people," said Julie Bataille, communications director for the rollout at the federal Health and Human Services Department.
The administration has done its own geographical research, drilling down even below the county level. Officials said the pattern coincides with the findings of AP's study, which was conducted by the State Health Access Data Assistance Center at the University of Minnesota.
With their own research, federal officials are focusing on 25 key metro areas. The top two are in Texas: Dallas and Houston. Next come Miami and Atlanta. In the Northeast, the northern New Jersey megalopolis and Philadelphia are on the list. Midwest markets include Detroit, Cleveland and Indianapolis. Southern cities also include Nashville, Tenn., and Charlotte, N.C.
The numbers help determine where to send HHS Secretary Kathleen Sebelius to pitch the law. They're guiding the placement of television ads aimed at younger people, scheduled to start airing as the Winter Olympics open this week.
Washington is largely steering clear of states that are leading their own sign-up efforts, such as California, New York and Illinois.
The research for the AP by the Minnesota health data center found that just 13 counties account for 20 percent of the uninsured. The top county, Los Angeles, has more than 2 million uninsured people, or about 5 percent of the national total.
"The administration is well aware of where the uninsured population lives," said Lynn Blewett, the center's director. "It's to their benefit to get out to the states where they are going to have the biggest bang for their buck."
Uninsured Americans generally live in major metro areas, but data-driven research can also help in rural states with seemingly low numbers of uninsured people, said Brett Fried, a senior researcher at the center. Census files that provide coverage information at the ZIP code level can be used to tease out concentrations of uninsured. Bataille said the government also has an outreach effort tailored to rural areas.
The Minnesota researchers used Census data from the 2011 Small Area Health Insurance Estimates, the only source of annual estimates of uninsured people for all counties. They were not able to filter out people who entered the country illegally and thus are not eligible for coverage under the law. Blewett said that group, although numerous, is not large enough to skew the overall geographic pattern.
High on the list of places with lots of uninsured people is Cook County, Ill., which includes Chicago. It ranks third nationally in the total number of uninsured, and third in uninsured young adults, with more than 460,000, the study found.
Among them is Katina Rapier, who recently filled out her paperwork during an Enroll America event at her community college. Enroll America is a nonprofit that works closely with the administration.
At 25, Rapier aspires to own a chain of women's clothing stores. But she's been uninsured since she turned 18 and says it's a struggle to afford her vitally important asthma medication. She thought she had missed the deadline to apply for coverage, not realizing that open enrollment runs through the end of March.
"If it can help me get safe medication, I'm all for it," Rapier said of the health care law.
No matter what the numbers say, she doesn't think the administration will have an easy time signing up young adults. "They think health is something that you worry about when you get older," Rapier said.
The White House originally set a goal of signing up 7 million people in the new insurance markets, and the administration says it has reached the 3 million mark. Website problems - federal as well as state - have cast doubt on whether original goal will be met.