When it was the Railroad and Warehouse Commission of Illinois, interlocking towers were assigned numbers, in the order in which they were registered with the Commission. This was similar to a numbering system adopted by the Railroad Commission of Texas, for that state. Except in Texas, the towers were actually officially known by the numbers. One of the more famous towers in Texas was "Tower 55", located near downtown Fort Worth.
In these lists, towers are grouped by year registered, and are listed in numerical order. The year registered is not necessarily the year constructed. Also identified are the railroads and the lines involved, which are explained through a separate link below.
Illinois Towers 1889-1899
Illinois Towers 1900-1913
Railroads And Lines
Some interlockings were later eliminated through grade separations.