Footing for a porch?
You definitely want your footings to extend below the frost line, otherwise as the ground freezes below your footing it will swell (as water does when it freezes) and the force of the swelling WILL push your footings out of position.

Ice breaks mountains - a porch doesn't stand a chance. :)  Dig DEEP.  With a frost line going as low as 4', I'd dig down 5.

However, that said, the FOOTING doesn't need to be 22" wide from 5' down all the way to the surface - a 22" by roughtly 12" deep footing put 5 feet down and a 6" or so wide reinforced wall coming up to surface would avoid the problems of freezing and save on concrete while offering structure.

This kind of work usually requires a permit as well, and its hard to conceal, so you might want a structural engineer to draw up proper approve-able plans.