Looks like a dead ringer for Chilocorus bipustulatus, but that sp. is listed on BugGuide as a European introduction found in N Am only in the San Joaquin Valley in CA. Which probably means it is something common on the East coast that I just haven't managed to find in BugGuide.
EDIT: No, it's Chilocorus bipustulatus all right! Thanks to Boris below & those on BugGuide ( bugguide.net/node/view/323817 ) who've been able to confirm the ID. Freaky! Literally: a freak find. It's not like I was trying!
This sp. is found well into Northern Europe, so it may be able to survive the winters here. It is used for biocontrol of scale insects, so perhaps it was released by a local green gardener. Or more likely it made its way cross-country with a load of produce. Shipping comes into the Port of Newark, ~10 mi away; Kearny, ~5 mi away, is a railyard, warehousing & distribution center. The entrance to the Lincoln Tunnel is less than a mile away. And my cousin (it's his house) makes regular trips to a local dairy, I think in upstate NY.
Incidental find in an urban backyard garden on underside of a leaf of a small shrub in the Rosaceae (I can find out what, if it matters; white flower spikes attracting bumblebees). 4.2 mm.
Will ya look at the balls on that squirrel! (Sorry, just couldn't resist.)
And yes, not long after, I bought a squirrel guard. Cute, but I couldn't afford to keep feeding them!
Native to eastern US, but introduced in Calif., and probably displacing the native species here.