Where were first steel mills in the United States built, and why these locations?

A few of the earliest steel mills in the United States operated in Alabama after the Civil War. There was a surplus of available labor due to the convict lease system and an agricultural depression.
Some of the largest and most famous steel mills at the turn of the nineteenth century operated in Pennsylvania. The western part of the state was closer to the iron ore mines found in Minnesota and Wisconsin and there was an abundance of anthracite coal, which is a high grade of coal that burns hot enough to remove most of iron's impurities. The western Pennsylvania region is close to the Great Lakes and many major Eastern railroads. The state is also a hub for European immigrants, especially those from Central and Eastern Europe.
While Alabama had some of the earliest mills, some of the more famous and profitable ones could be found in Pennsylvania.