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 times the growth rate in the rest of the country.

Why has Lee County been so resilient? One of the biggest reasons is that it is home to a major college town.

During the manufacturing downturn that began in the late 1990s, Auburn University in Auburn, Ala., provided a steady source of employment, improved the nimbleness of the local workforce and helped attract new businesses to replace those that fled when times got tough.

In 2014, General Electric Co. chose its new plant in Auburn as the company’s first to use 3-D printing to make high-volume products. Thirty printers that look like a row of commercial pizza ovens build thousands of jet-engine nozzles a year, tended by a few technicians in lab coats.