HERE Maps / HERE WeGo (whatever the hell it's called now) has supported offline map downloads from day one, between every Windows / iOS / Android phone I've owned I have had the entire US downloaded from day 1.
+1 for maps.me, I've been using it for more than a year in multiple European countries and it's been rock solid, even if it sometimes takes a while to get a fix (though that's probably more of a problem with my phone than with the app).
Google Maps also supports offline downloads, but from what I remember, they expire every 30 days, so you need to keep re-downloading.