Complex sentence: Monticello Railway Museum is a non-profit organization located in Monticello, Illinois, operating excursion trains over track formerly used by the Illinois Terminal and Illinois Central Gulf.
Split into simpler sentences: Monticello Railway Museum is a non-profit railroad museum located in Monticello, Illinois. The museum also has a heritage railroad which operates excursion trains over a former railroad line that was owned by Illinois Terminal and Illinois Central Gulf.