That sounds about right subjectively. What might not be obvious from overseas, or even to Americans who've never been to Maryland, though, is how unevenly populated Maryland is.
The "Northeast Corridor" in particular is used in context to an Amtrak line (
https://en.wikipedia.org/wiki/Northeast_Corridor) which runs from Washington D.C. to New York City, the most densely populated section of the U.S., and on up to Boston. It's really the cities along that rail route that comprise a densely populated conglomeration, of the type that "infinite city sprawl" in Civ, especially earlier Civ versions, can evoke. You leave the DC metro area, before long you hit Baltimore, on a northern suburb of Baltimore you reach Firaxis's headquarters-town, it isn't much longer and you are in Philadelphia, then Wilmington Delaware, then the cities of Jersey, and then New York City. It isn't literally all contiguous city, but it's the closest equivalent to it in the U.S.
(I'd be curious how it compares demographically to, say, Amsterdam to Paris, a route I traveled once at a leisurely and not-entirely-direct pace. I'm sure NY to DC can't compete on quality of beer, but it might compete on density)
Meanwhile, western and eastern Maryland are empty. I love western Maryland, they've got mountains, forest, farms, a great place for an outdoorsy vacation. Eastern Maryland, across the Chesapeake Bay, is also fairly empty, but in a more farms/fishing/waterfront manner. DC Metro and Baltimore are the big cities, but even the mid-size ones like Annapolis, Frederick, and Hagerstown are more or less in the center part of the state.
So it means that the most densely populated counties in Maryland have densities of 530, 806, and 2375 per square kilometer, while the least densely populated are about 17 per square kilometer. Huge variations. As there are in France, the country among those you've listed that I've done the most demographic research about.
Admittedly also a pedantic point, but as a fan of Maryland, I didn't want the Internet's impression of it as being anywhere near uniform. And I suppose it supports the argument that there should be open areas, since even in a small state with two large metro areas, there are significant wide-open spaces.