Chicago
VS.
Los Angeles
Year City Population Growth City Population Growth Notes
larger city in
bold
1850
Chicago 29,963 570.3% Los Angeles 1,610 1st Los Angeles census
1860
Chicago 112,172 274.4% Los Angeles 4,385 172.4%
1870
Chicago 298,977 166.5% Los Angeles 5,728 30.6%
1880
Chicago 503,185 68.3% Los Angeles 11,183 95.2% Los Angeles' growth rate exceeds Chicago's for the first time and remains so till today.
1890
Chicago 1,099,850 118.6% Los Angeles 50,395 350.6% Chicago becomes the second largest city in the United States.
1900
Chicago 1,698,575 54.4% Los Angeles 102,479 103.4%
1910
Chicago 2,185,283 28.7% Los Angeles 319,198 211.5%
1920
Chicago 2,701,705 23.6% Los Angeles 576,673 80.7%
1930
Chicago 3,376,438 25.0% Los Angeles 1,238,048 114.7%
1940
Chicago 3,396,808 0.6% Los Angeles 1,504,277 21.5%
1950
Chicago 3,620,962 6.6% Los Angeles 1,970,358 31.0%
1960
Chicago 3,550,404 −1.9% Los Angeles 2,479,015 25.8%
1970
Chicago 3,366,957 −5.2% Los Angeles 2,816,061 13.6%
1980
Chicago 3,005,072 −10.7% Los Angeles 2,966,850 5.4% Chicago is just barely larger than Los Angeles and the latter would become the second largest city in the United States in the early 1980's.
1990 Chicago 2,783,726 −7.4%
Los Angeles 3,485,398 17.5% Los Angeles is officially the second largest city in the United States with this census.
2000 Chicago 2,896,016 4.0%
Los Angeles 3,694,820 6.0% Los Angeles surpasses Chicago's 1950 peak population.
2010 Chicago 2,695,598 −6.9%
Los Angeles 3,792,621 2.6% Chicago experiences population decline after gain in 2000 census and Los Angeles has the lowest growth rate in it's history.
This is no doubt the largest city vs. city power shift in American history. As others have said even though New York City and Chicago share a common history in many ways there was never any real danger of a change in the positions of power. The Chicago vs. Los Angeles shift represented the change in American culture from relatively high density and centralized cities in the northeast and Midwest to relatively low density and decentralized cities in the sunbelt. Also I don't think before Los Angeles became the second largest city there was that much of a bi-coastal elitism, i.e. the coasts vs. the rest of the country. Prior to World War II and for a time afterwards it was more east vs. west, north vs. south or if anything New York City vs. everyone else. Chicago was pretty well respected as a cultural and economic powerhouse and if anything the west coast was kind of looked down upon by city dwellers east of the Mississippi. A classic example of this attitude was Al Smith's famous statement that he would rather be a lamppost on Park Avenue in New York City than the Governor of California.