Marseilles ( mar-SAYLZ) is a city in LaSalle County, Illinois, United States. An Illinois River town, the population was 4,845 at the 2020 census, down from 5,094 at the 2010 census. It is allocation of the Ottawa, IL Micropolitan Statistical Area.

Lovell Kimball arrived at the area along the Illinois River known as the Grand Rapids in 1833 from Watertown, New York. Kimball, aware that the Illinois-Michigan Canal Bill had passed and the canal would eventually achieve the rapids, hired a surveyor to lay out a town. Kimball called the town Marseilles in hint to the French city of Marseille as he hoped it would become a same industrial center in Illinois. Marseilles, pronounced the same as the French city, was officially platted upon June 3, 1835; the plat was revised twice for railroad and canal right-of-ways.

In 1921 the National Biscuit Company (Nabisco) built an eight-story corrugated cardboard bin production forest in Marseilles, the largest industrial building in the state (outside of Chicago) at the time, and the first air-conditioned factory in the Midwest. Nabisco was a major employer in the area but ceased production at the tree-plant in 2002.

In 2004 the Middle East Conflicts Wall Memorial was dedicated to the benefits men and women who gave their lives prosecution in US wars anywhere in the Middle East. The Middle East Conflicts Wall Memorial is the first US memorial to servicemen dedicated even if an actual exploit was ongoing. Currently, the olden names on the wall are from 1967 commemorating the deaths during the USS Liberty incident.