I used to have this problem every year until I found out it was because of the female boxelder tree I had in my front yard.....Do you live in Lisle by any chance the town is filled with them....lol Ok so what did I do I had the tree cut down and no more box elder bugs on my house....they have all moved to the guy next door who has about 20 of them lining the side of his yard....lol
Oh also I have tried all the suggestions below they are a waste of time and they always come back. I did however find a spray solution in a green bottle at Kmart a couple years back it was some flying insect killer spray...seemed to work longer than all the rest of them.