A tiny frontier settlement for the first few decades of the nineteenth century, Chicago had a population of scarcely 50 in 1830 and less than 4,200 at the time of its incorporation in 1837. By 1850 the population was 29,963, and was nearly ten times that (298,977) by 1870. It surpassed half a million (503,298) by 1880, a million (1,098,570) a decade later, by which time Chicago was larger than any American city except New York.

Chicago was sixty times bigger in 1900 (1,698,575) than it had been fifty years earlier. Its geographical dimensions also increased markedly in this period, from approximately 35 square miles at the time of the Great Fire of 1871 to some 185 square miles by the 1890s.

A large portion of the multitudes who arrived in Chicago were native-born Americans who had left countless farms, villages, small towns, and other cities. But an enormous and unprecedented percentage of new Chicagoans came not only from abroad, but also from countries that had provided few immigrants to the United States until the 1840s. In 1870, over 48 percent of Chicagoans were foreign-born, and, while this figure dropped to just over 40 percent in the period between 1880 and 1890, the absolute number of settlers from abroad increased enormously.

This population as a whole was overwhelmingly white—less than 2 percent of Chicagoans were African American, and there was only a trace of recent arrivals from Asia. By the 1890s an increasing percentage of the immigrant population derived from Scandinavia and from southern and eastern Europe, but the major countries of origin remained Germany and Ireland. Chicago in 1890 included over 170,000 inhabitants born in Germany, as well as almost 70,000 born in Ireland.

By 1880, over 208,000 of Chicago's 458,313 employed persons worked in occupations defined as manufacturing and mechanical, with 62,995 in trade, the next largest category. Chicago's most rapidly growing area of employment was clerical services, with 41,105 workers (almost forty times the number in this category a decade earlier). But while the native-born comprised over 73 percent of these clerical workers (and a similar percentage of those in more prestigious white-collar occupations), over 136,000 of those employed in manufacturing—more than 65 percent—were immigrants. A considerably higher percentage had at least one parent from abroad.