"Second City" - By one possible etymology, this refers to the fact that Chicago had the second largest metropolitan area in the United States for most of the 20th century (Los Angeles is now larger). Alternatively, it may refer to the rebuilding of the city between the Great Chicago Fire of 1871 and the World's Columbian Exposition of 1893.
"City of Big Shoulders" - This nickname is taken from the fifth line of Carl Sandburg's poem "Chicago".
"City by the Lake" - Used as early as the 1890s.
"City in a Garden" - English translation of the Latin motto on the city seal: "Urbs in Horto"
"The City that Works" - A slogan from Mayor Richard J. Daley's tenure as mayor, describing Chicago as a blue-collar, hard-working city, which ran relatively smoothly.