Can I chop up and freeze mirepoix raw, or do the vegetables have to be blanched first? Thanks!
Yes, you can freeze mirepoix, but it'll be pretty soft once defrosted, as Peter V noted. Onions and celery do not freeze well, though carrots do okay.
All three vegetables, when whole, should be blanched for a few minutes before freezing. For vegetable-specific freezing instructions see the National Center for Home Food Preservation's Freezing Guide.
It's best to use fresh, but blanched for 1-2 minutes then frozen works okay. I do not blanch diced vegetables for more than 2 minutes.
What will you be doing with this mirepoix?
If it's just going to be a basis for a stock, you could probably freeze it without ill effect.
If you're going to be caramelizing it in some butter, and then using it in a final dish, I'm not sure that I would freeze it; the veggies seem likely to get mushy, regardless of whether or not they were blanched first.