OPELIKA, Ala.—Lee County, Ala., lost 7,000 jobs in industries from textiles to tires to fitness equipment when Chinese competition invaded America. Vacant storefronts dotted downtown Opelika, the county seat, and disability claims soared as older workers with limited skills struggled to find new jobs.

Instead of merely surviving, though, Lee County is now thriving. Its unemployment rate of 4.7% in October was slightly lower than for the U.S. as a whole. Since 2001, the east-central Alabama county has added 14,000 jobs, five...