Roswell B. Mason (September 19, 1805 – January 1, 1892) served as mayor of Chicago, Illinois (1869–1871) for the Citizens Party.

[1] His mother was a lineal descendant of Roger Williams, the founder of Rhode Island.

[3] Mason held a high position with the Illinois Central Railroad until he decided to run to be Mayor of Chicago.

Mason responded by directing General Philip Sheridan to place the city under martial law.

Mason's tenure as mayor ended on December 4, 1871, when he was succeeded by Joseph Medill.