July 4 hot dogs likely from Iowa WASHINGTON, July 4 (UPI) -- The U.S. Census Bureau said there is a 1 in 3 chance the hot dogs at a Fourth of July cookout came from Iowa. The bureau said there is about a 33 percent chance the hot dogs and pork sausages originated from one of the 19.7 million pigs and hogs catalogued in Iowa in March 2012. The agency also said the estimated U.S. population Wednesday was 313.9 million, a vast increase from the estimated 2.5 million when the Declaration of Independence was signed in 1776. The Census Bureau said July 4 is also a good day for China, with $3.3 million worth of U.S. flags imported from the country each year and $223.6 million worth of fireworks imported from China annually.