WASHINGTON (MarketWatch) -- Texas will gain four seats, Florida will gain two seats and New York will lose two in the U.S. House of Representatives as the Census Department revealed results from the 2010 Census, which showed the U.S. population growing 9.7% to 308.7 million people. The fastest growth over the decade came in the South and the West, with Michigan actually showing a population decline. In all, 12 seats are changing hands in the House.