Moved from Hippodamia.

Exact match to figure 190, a variation of Hippodamia caseyi, in E. Chapin's guide to Nearctic Hippodamia.(1) It's dead-on: the lateral extension of the medial black area on the pronotum, the reduced but slightly convergent white lines on the center of the pronotum, and the size, location, and confluence of the elytral maculae.

I don't see anything quite like it in any of Chapin's figures for other Hippodamia species; the species are so variable it's hard to say anything for certain, though. But if I had to bet, it'd be H. caseyi.

Moved from Lady Beetles.

Moved from Beetles.

The black band across the pronotum, which interrupts the white margin but doesn't cut it off from the elytra, will probably be a key to ID. Many Hippodamia species have a complete white margin, and a few have partial margins that don't reach the elytra at all.

Species w/ interrupted margins in your area include H. caseyi and H. quinquesignata, but I'm not very familiar w/ northern/western species. Try moving this to the Coccinellidae or Hippodamia pages, where the lady beetle experts are more likely to see it - there are some massive threads about northwestern Hippodamia!