Yup, you've got boxelders!

We just had the same issue at our house. They were all over the windows, doors...anyplace that was warm, and every time I opened the door a dozen of them would get in. I've been keeping a vacuum cleaner stationed by the door.

We had an exterminator come on Monday, he inspected the property and found a colony in the wall that lines our driveway - literally hundreds of them coming in and out. He sprayed the living shit out of it and intends to come back again this coming Monday, but once he sprayed they've all but disappeared.

I might recommend you take a walk around your property and see if there's a nearby colony.