In Fort Mill, a city of 10,000 residents about 20 miles south of Charlotte, N.C., local leaders saw the subprime-mortgage industry as a way to help retool the economy from its withered roots in the textile industry. But more than 700 jobs at Senderra, HSBC Holdings PLC and other mortgage operations that popped up during the housing bubble have since disappeared or moved away. Unemployment in Lancaster County, where Senderra got a tax break as a job-creation incentive, hit 18% in November, the latest month for which figures are available. The U.S. unemployment rate was 10% in December.