Why do I have ants in the middle of winter?

I had the worse season of ants this past summer, they were in every area of my home. And now, sporatically throughout the winter (which it has been the coldest, snowiest one in DE) I STILL am getting them in sporatic areas, all over my house. Today they are all over my kitchen counter and in my family room on the hardwood floor and my husbands side table. They also are found in the bathrooms, my son's bedroom, my office.......... Oh I'm so disgusted! And we use terro, over and over and over.