In the mid-1800s, most of America's industry was located where?
Most industry was located in the Northeast of the United States.
The main reason that why industry was mostly in the Northeast is because the West and South had their own specializations. The South was 'Cotton King,' meaning that much of the South was focused on cotton plantations. The West focused on growing crops like wheat and corn. Thus, the Northeast became the industrial center that obtained materials from the other areas of the United States to process those materials and manufacture goods.