I'd have to check my list for the exact count, but something in the neighborhood of 28-32.
Grew up on the East coast, so everything south of Pennsylvania including Gulf Coast. Picked up some midwest in my travels (Michigan, Ohio, Wisconsin) Then drove cross country to Oregon and picked up quite a few on the way Missouri, Iowa, Nebraska, Wyoming, Utah, Idaho. Then the whole west coast Washington and California shortly after I moved out here. Now that I live on the West coast hope to pick up Alaska and/or Hawaii fairly soon.
I want to hit all 50 but I have a hard time finding a reason to visit North Dakota.