It looks like your plant has septoria leaf spot or early blight (or both). These diseases are common on tomato plants in Minnesota. They are worse some years than others. These fungal diseases are in the soil and the soil splashes up onto the plants.
Prevention is the best way to deal with these diseases. Don't water overhead or at night (I see a soaker hose in the photo, which is good). Keep the plants off the ground by staking them (it looks like yours are sprawling on the ground). Mulch around them to keep rain from splashing up. Provide plenty of air circulation around the plants by pruning off suckers and staking them. Don't work around them when they are wet. Clean out the debris in the fall, and don't compost it. Don't plant tomatoes in the same spot year after year. You can read about these diseases here: