Complex sentence: On July 22,1882, six of Danville's enterprising citizens founded the Riverside Cotton Mills, which was in its day known the country over as Dan River Inc., the largest single-unit textile mill in the world.
Split into simpler sentences: On July 22,1882, six of Danville's citizens founded the Riverside Cotton Mills. In its day it was known nationally as Dan River Inc., the largest single-unit textile mill in the world.