It stated 1979 as the previous peak of manufacturing, and they're now at twice that level. I presume they're no longer making cheap, consumer products, but are more focused on industrial , aerospace, automotive, technology, etc. And it was clear that the new manufacturing is not going to the small urban and rural areas but the big cities. That helps account for why those areas are still economically depressed. Plus the new manufacturing is not as labour intensive but requires skills that need post-secondary education.
Except the manufacturing sector has not declined. Only the number of jobs in in it has. The biggest decline in jobs happened after 2001. On the other hand, the tech sector continues to grow in both total production/dollars and employment.