Travis County added 31,739 residents between July 1, 2006 and July 1, 2007 according to estimates released today by the U.S. Census Bureau. Only eight counties in the country added more, including four in Texas (Harris, Tarrant, Bexar and Collin). On a percentage basis, Williamson and Hays counties were among the fifteen fastest growing counties and Travis was in the top 100....