In good economic times or bad, the story never changes in the central San Joaquin Valley -- on average, its residents are among the poorest in California and the nation.New data from the U.S. Census Bureau drove that point home Tuesday.In 2007, the bureau's American Community Survey listed Tulare County as having a higher percentage of people living in poverty than any other California county of the 40 for which data were available. Almost 24% of that county's residents lived in households where the income was below poverty level. Second worse in the state was Imperial County, with nearly 22%.Only five U.S. counties with 250,000 or more people ranked higher in poverty. Three were along the border between Texas and Mexico, one was the Bronx in New York City, and the fifth was Philadelphia County, Pa.Other Valley counties fared little better in the state rankings. Fresno County was in fourth place, with 20% of its people -- one in five -- living in poverty last year.Merced's rate was 19.4% and Madera was 14.5%. The one bright spot in the data was Kings County, where the estimated poverty rate dropped from 21.3% in 2005 to 15.1% last year.Jay Salyer, economic development manager for the Kings County Economic Development Corporation, was mystified by that county's numbers, despite what he called strong hiring by local businesses."That's a big decrease," he said. "I really don't have anything right now that I could put my finger on to say this is what happened."In each of the other central San Joaquin Valley counties, the year-to-year changes appeared to be below the level of statistical significance.Wells Fargo senior economist Gary Schlossberg said the bleak numbers may simply reflect the region's mix of jobs, which tend to be low-paying, and its labor force, which is less likely to consist of U.S. citizens or other legal residents."To the extent that you are drawing in more agribusiness workers or even undocumented construction workers, that could be having an effect," he said.The definition of poverty varies by household size and number of children, as well as the month that the household was surveyed. In the case of a family of four, including two children, surveyed in January 2007, poverty would be defined as an annual income of less than $20,435.In a separate report Tuesday, the Census Bureau said that despite little change in poverty rates, the number of Americans without health insurance declined from 47 million in 2006 to 45.7 million in 2007. Year-to-year changes by state were not provided, but comparing the 2004-05 period with 2006-07, California showed no significant difference.The percentage of people covered by health insurance provided by employers actually declined between 2006 and 2007, but the number covered by government-provided insurance such as Medicare or Medicaid/MediCal rose.