Five years ago, entry-level candidates could expect to earn nine bucks an hour at a Haworth Inc. office-furniture factory. The economy was humming, but job growth was choppy, and wage gains anemic.

Things changed, though, as average unemployment in the counties where Haworth makes products like movable walls, desk chairs and storage cabinets tumbled from 6.3% in 2014 to 3.6% last year. Today’s newcomer makes $12.50 an hour.

Pay...