The Île de France region consisting of Paris and its suburbs contains 11.7 million residents at a population density of about 2,500 people per square mile. The closest match in North America (and it’s a pretty close match) turns out to be the Los Angeles / Long Beach / Santa Ana Metropolitan Statistical Area comprised of LA County and Orange County. It contains 12.8 million people living at a population density of about 2,650 per square mile.
I’m not really sure what conclusion I’d draw from that other than a reminder that average population density stats don’t necessarily tell you all that much about the character of an urban area. I’d also say that in my experience, the underrated LA Metro is a considerably more pleasant rider experience than its (dirty, bad wayfinding) Paris counterpart, though obviously Paris Metro has LA beat massively in terms of actual coverage area. The actual Paris municipality, however, is incredibly dense. Indeed, much denser than any substantial American municipality. If Manhattan were a freestanding city, it would be denser than Paris, but Paris is much denser than Brooklyn or than New York City overall. The kind of weighted density stats that capture this idea of an LA-level of density with a super-dense core are harder to look up, but probably much more valuable.