Looks like it’s 380 in the Swiss Plateau (you might be mixing up sq km and sq mi), which puts its at about ~70% of the population density of the Netherlands as a whole.
https://en.wikipedia.org/wiki/Swiss_Plateau
Fair, I had a quick look, 600-700 is likely for the big cities areas.
Fair, I had a quick look, 600-700 is likely for the big cities areas.