Mississippi's rate was more than 60 percent higher than the national average in 2006, the U.S. Centers for Disease Control and Prevention said. The teen pregnancy rate in Texas and New Mexico was more than 50 percent higher.
The three states have large proportions of black and Hispanic teenagers - groups that traditionally have higher birth rates, experts noted.
The lowest teen birth rates continue to be in New England, where three states have teen birth rates at just half the national average.
It's not clear why Mississippi surged into first place. The state's one-year increase of nearly 1,000 teen births could be a statistical blip, said Ron Cossman, a Mississippi State University researcher who focuses on children's health statistics.
More than a year ago, a preliminary report on the 2006 data revealed that the U.S. teen birth rate had risen for the first time in about 15 years. But the new numbers provide the first state-by-state information on the increase.
The new report is based on a review of all the birth certificates in 2006. Significant increases in teen birth rates were noted in 26 states.
"It's pretty much across the board" nationally, said Brady Hamilton, a CDC statistician who worked on the report.
Numerically, the largest increases were in the states with the largest populations. California, Texas and Florida together generated almost 30 percent of the nation's extra teen births in 2006.
Some experts have blamed the national increase on increased federal funding for abstinence-only health education that does not teach teens how to use condoms and other contraception. They said that would explain why teen birth rate increases have been detected across much of the country and not just in a few spots.
There is debate about that, however. Some conservative organizations have argued that contraceptive-focused sex education is still common, and that the new teen birth numbers reflect it is failing.
Other factors include the escalating cost of some types of birth control and their unavailability in some communities, said Stephanie Birch, who directs maternal and child health programs for the Alaska Department of Health and Social Services.
Glowing media portrayals of celebrity pregnancies don't help, either, she said. "They make it out to be very glamorous," said Birch, who cited a calculation by Alaska officials that teen pregnancies were up 6 percent in that state in 2006.
In Mississippi, there were about 68 births for every 1,000 women, ages 15 through 19 in 2006. The New Mexico rate was 64 per 1,000; Texas was 63.
The national birth rate for females in that age group was about 42 per 1,000. New Hampshire, with a rate of 19 per 1,000, was the nation's lowest.
A variety of factors influence teen pregnancy rates, including culture, poverty and racial demographics. For those and other reasons, kids in mostly white New England likely would delay child birth, said David Landry, a researcher at the Guttmacher Institute, a New York-based organization which supports abortion rights and gathers research on sexual and reproductive health.
"It's more costly for youth in the Northeast to have a teen birth than for youth in the South, in terms of opportunities they'll miss," he said.