The Alton and Southern Railway (reporting mark ALS) is a switching railroad in the Greater St. Louis area in Illinois.

It is a wholly owned subsidiary of the Union Pacific Railroad.

Alcoa sold the line to the Missouri Pacific Railroad and Chicago and North Western Railway (CNW) in 1968,[1] and it was reorganized as the Alton and Southern Railway.

In 1972, CNW's share was sold to the St. Louis Southwestern Railway.

The Alton and Southern is still a legally separate entity but is wholly owned by UP.