NEW YORK (CNNMoney.com) – Roughly 12.5 percent of the U.S. population is living in poverty, according to data released recently from the Census Bureau.

Among kids under 18, the poor represent an even higher percentage: 17.6 percent.

In 2003 – the latest year for which Census data are available – a total of between 35.2 million and 36.5 million people fell under the poverty threshold.

That threshold varies depending on family size. In 2003, a single person making less than $9,393 a year and a family of eight making less than about $35,572 are both considered poor.

The oft-used example of a family of four is considered poor if they live on less than $18,660.

The national median income in 2003 was $43,318.

But the percentage of the population that is poor varies widely state by state.

The states with the highest percentage of poor residents relative to the state's total population were: Mississippi (18.3 percent), Louisiana (18.1 percent), New Mexico (17.7 percent), West Virginia (16.3 percent), and Texas (16.2 percent). In the District of Columbia, the poor represented 17.5 percent of the population.

The list is similar for states with the highest population of kids under 18 who are poor: Mississippi (26.8 percent); Louisiana (26.6 percent); New Mexico (25.9 percent); West Virginia (24.4 percent); Arkansas (23.5 percent); and Texas (22.8 percent).

The District of Columbia trumps them all, though, with a full 29.6 percent of its child population living below the poverty line.

Those percentages don't count foster kids, or children in delinquent centers or other institutions, said David Waddington, chief of Small Area Estimates at the Census Bureau.

The Census poverty data also drill down into counties and school districts. The school district numbers are used to help determine the distribution of federal education funding, Waddington said.

The poverty thresholds, it should be noted, do not account for cost-of-living differences in different states. So a family of four making less than $18,660 a year would be considered impoverished whether they lived in El Paso, Texas or in New York, New York.