Complex sentence: People of Norwegian and Swedish descent both stood at about 20,000 each, while people of Czech, Lithuanian, Portuguese, Scotch-Irish, and Welsh descent all numbered between 12,000--14,000 people.
Split into simpler sentences: People of Norwegian and Swedish descent both stood at about 20,000 each. Lastly, people of Czech, Lithuanian, Portuguese, Scotch-Irish, and Welsh descent all numbered between 12,000--14,000 people.