Before 1865, where were most of the railroad tracks in the United States concentrated?

By far, most of the nation's rail industry was located in the North. This is not surprising, as most of the nation's industry and manpower were also there. Railroads linked the major cities of the North, and several rail lines were finding profits in moving farm products from the Midwest to the East. In many places, rails were even starting to replace canals as the preferred means to move goods.
Before the Civil War, Congress considered the best route for a transcontinental railroad. Jefferson Davis proposed a Southern route that would use Mississippi, his home state. Stephen Douglas used Illinois as the origin for a rival route. The war happened before construction could begin, thus making the northern route the obvious choice for the nation. However, since most of the major railroads were in the North, it is most likely that the nation would have chosen the northerly route for its longest railroad.