One year before the Great Chicago Fire, the 1870 Census counted 298,977 people living in Chicago, Illinois. Despite the loss of so many homes and businesses, residents quickly rebuilt, and 503,185 people lived in the city in 1880. The population reached 1,099,850 in 1890, 2,185,283 in 1910, and 3,376,438 in 1930. Chicago's population peaked at 3,620,962 in 1950. At the time of the 2020 Census, Chicago was the nation's third-largest city, with 2,746,388 people calling the city home.

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With a population of 298,977 at the time of the 1870 Census, Chicago was the fifth-largest city in the United States. Perhaps as many as 90 percent of the city's population lived in wood-framed and -roofed houses. The city earned the nickname "Mud City" early in its history and Chicagoans avoided the mud- and manure-filled streets by using wooden sidewalks and bridges that connected homes, businesses, schools, and churches. In the autumn of 1871, all that wood was tinder-dry, as the period from July 3 until October 8, 1871 remains the driest period in Chicago's history. During that time, a meager 3.70 inches of rain fell. With the last measurable rain falling on September 28 (.11 inches), low humidity, and a steady 20 mph wind from the southwest, Chicago was just a spark away from an inferno.

Weary firefighters had successfully battled numerous small blazes throughout the city in early October 1871. However, at about 8:30 p.m. on October 8, a fire in a barn owned by Patrick and Catherine O'Leary at 137 De Koven Street had fully engulfed several buildings before help could arrive. Neighbors scrambled to douse the flames as wind-swept embers showered down upon the neighborhood's wood shingle and flammable tar roofs. Super-heated winds helped the fire jump the South Branch of the Chicago River by midnight and destroyed the city's gasworks. By 2:00 a.m. on October 9, the courthouse was ablaze. When the waterworks building caught fire, its pumps shut down and firefighters' hoses went dry throughout the city. Terrified Chicagoans fled from their homes, with some wading into Lake Michigan as the flames ripped through buildings along the waterfront.

The fire showed no signs of slowing as the sun rose on October 9. City officials called upon General Philip Sheridan, who was living in Chicago at that time. Sheridan ordered his men to dynamite buildings in the fire's path hoping to slow its advance. The fire began to subside on the evening of October 10 after it exhausted the abundant fuel in the densely populated sections of the city and moved into the more open "North Side" of Chicago. Much to the relief of firefighters and exhausted volunteers, a light rain fell through the night, which helped to douse hot spots.

Chicagoans waited days for the smoldering ruins to cool before attempting to access the damage and salvage their possessions. In total, the fire destroyed an area of homes and businesses exceeding 2,000 acres—an expanse more than twice the size of New York City's Central Park. Approximately 17,500 buildings were destroyed, 90,000 people were homeless, and as many as 300 died. Despite the devastation, Chicago quickly rose from the ashes stronger than ever before. Between 1870 and 1880, the city's population grew from 298,977 to 503,185, making it the nation's fourth largest city. Ten years later, the population more than doubled to 1,099,850. Wooden buildings were replaced with structures built with fire-resistant iron, brick, and reinforced concrete, including the world's first "skyscraper"—the 10-story tall Home Insurance Building built in 1885. Today, Chicago is a leader in finance, culture, industry, transportation, education, tourism, sports, and technological innovation. With a population of 2,746,,388 in 2020, it remains one of the largest cities in the United States behind New York City, NY, and Los Angeles, CA.

You can learn more about Chicago and the 1871 "Great Chicago Fire" using census data and records. For example:

• The name "Chicago" was first recorded in 1688 by French soldier Henri Joutel during a Mississippi River expedition led by Rene-Robert Cavelier, Sieur de La Salle. Joutel wrote the name as "Chicagou"—the Algonquian word meaning "onion" or "garlic field." At that time, Algonquian-speaking American Indians lived throughout New England, the Midwestern United States and the Canadian prairies. These groups included the Menominee, Shawnee, Kickapoo, Cheyenne, and Nipmuc tribes. Another Algonquian tribe—the Wampanoags from eastern Massachusetts—participated in one of the American colonies' first Thanksgiving celebrations with the Plymouth Colony's Pilgrims in 1621. In 2019, the American Community Survey found that people of Algonquian ancestry were part of the 5,665,200 Americans who identify as American Indian and Alaska Native alone or in combination with one or more other races. 
• The 1840 Census was the first to include Chicago. In that year, Chicago's population was 4,470. The city's population grew to 29,963 in 1850; 112,172 in 1860; 298,977 in 1870; and 503,185 in 1880. Chicago was the United States' second-largest city following the 1890 Census, with a population of 1,099,850, and retained that title until being surpassed by Los Angeles, California, in 1990. With a population of 2,746,388 in 2020, Chicago is currently the nation's third-largest city behind New York City, New York (8,804,190), and Los Angeles (3,898,747).
• Many Americans assume Chicago earned its nickname as the "Windy City" for the strong, chilly winds that sweep into the city from Lake Michigan. However, Chicago doesn't typically make the list of windiest cities in the United States. Fargo, North Dakota, Concordia, Kansas, Boston, Massachusetts, Kahului, Hawaii, and Kaktovik, Alaska, are just a few of the many cities and towns that are windier than Illinois' famous "Windy City." According to the National Oceanic and Atmospheric Administration, New Hampshire's Mount Washington registered a record-setting wind gust of 231 mph on April 12, 1934, a record that stod until 1996, when Tropical Cyclone Olivia produced a 253 mph gust on Barrow Island, Australia. Given that Chicago's winds are relatively calm in comparison, the city likely earned its "Windy City" moniker from "long-winded" 19th-century residents and politicians who bloviated about their city as they sought to host the 1893 World's Fair and competed for business and industrial investment with aspiring Midwestern cities like Cincinnati, Ohio, Detroit, Michigan, and St. Louis, Missouri.
• The Chicago Fire Department was established on August 2, 1858, when the Chicago City Council replaced the volunteer fire department with one staffed by paid firefighters. At the time of the 1871 Great Chicago Fire, the city of Chicago employed just 185 firefighters. Today, the Chicago Fire Department employs more than 4,500 firefighters and paramedics, and the site where the 1871 fire began is now home to Chicago's Robert J. Quinn Fire Academy. A plaque at the academy marks the exact spot where Patrick and Catherine O'Leary's barn once stood.
• The Census Bureau did not report the number of people working as professional firefighters until 1900. In that year, 14,576 people worked as firemen in the United States. The number grew to 35,606 in 1910, 50,771 in 1920, and 73,008 in 1930. In 2019, the U.S. Fire Administration reported there were 1,291,500 fires in the United States, many of which were contained by the 324,620 men and women working as firefighters in the United States. In 2019, the Bureau of Labor Statistics reported that the mean annual salary for the nation's firefighters was $54,650.
• In 1922, the Census Bureau opened a permanent regional office in Chicago (along with offices in New York and Los Angeles) to assist with the 1930 Census. Today, the Chicago Regional Office assists with the agency's censuses and surveys, data dissemination, and geographic operations in Arkansas, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, and Wisconsin—representing a population of more than 53 million.
• Many American cities suffered devastating fires in their histories. For example, an 1838 fire in Charleston, South Carolina, may have resulted in the city's population declining from 30,289 in 1830 to 29,261 in 1840. Boston suffered several "great" fires, including blazes in 1711, 1769, 1787, and 1872. The 1872 fire was the most severe, destroying 776 buildings and killing 13 people. Paris, Texas, suffered considerable damage from three fires in 1877, 1896, and 1916. In 1889, Spokane, Washington, firefighters were forced to demolish buildings with dynamite to slow advancing flames after they lost water pressure to their hoses. A 1901 fire in Jacksonville, Florida, destroyed nearly 2,400 buildings, killed 7 people, and remains the third-worst urban fire in the United States following the 1871 Chicago Fire, and the fire associated with the 1906 San Francisco earthquake. A 1904 fire in Baltimore, Maryland, destroyed 1,500 buildings in the city's harbor and business districts. When firefighters from neighboring states arrived to help fight the fire, they discovered that their equipment was not compatible with Baltimore's hydrants, hoses, and equipment. Following the Baltimore fire, the National Fire Protection Association adopted a national standard for fire hydrants and hose connections.
• A number of "Famous and Infamous" Americans have called Chicago home including—animator Walt Disney, crime boss Alphonse Capone, actor Jason Robards, Lee Harvey Oswald's killer Jack Ruby, comedian Jack Benny, bandleader Benny Goodman, First Ladies of the United States Betty Ford and Michelle Obama, radio personality and writer Jean Shepherd, novelist John Dos Passos, Rudolph the Red-Nosed Reindeer author Robert L. May, baseball team owner Charles Comiskey, chewing gum tycoon William Wrigley, Jr., serial killer H.H. Holmes, and Chicago Cubs baseball player Ernie Banks.
• Until the mid-1900s, Chicago was famous as the nation's hub for livestock slaughtering and meatpacking. After World War II, Chicago's meatpackers began moving to other areas of the country. Today, the Bureau of Labor Statistics reports that Texas, North Carolina, Iowa, Minnesota, and California lead the nation for employment in slaughterhouses and meat packing facilities. In 2017, Chicago's Professional, Scientific, and Technical Services sector (NAICS 54) led all other sectors in the city having 10,735 establishments with sales, value of shipments, or revenue totaling more than $48.1 billion. With 2,245 establishments, the Merchant Wholesalers (except Manufacturers' Sales Branches and Offices) in Chicago's Wholesale Sector (NAICS 42) recorded more than $40.4 billion in sales that same year, followed by 6,945 Retail Trade establishments (NAICS 44-45) with $23.3 billion, and the Health Care and Social Assistance sector's 6,778 establishments earning $22.9 billion.

Between May 1 and October 30, 1893, Chicago hosted the 1893 World's Fair at Jackson Park—a 1,055-acre park designed by Frederick Law Olmsted and Calvert Vaux on the shores of Lake Michigan.

Along with attractions such as George Washington Gale Ferris, Jr.'s "Ferris Wheel," exhibits sponsored by 46 countries, and concession stands that introduced new foods like hamburgers, hot dogs, cotton candy, and ice cream cones, many of the fair's estimated 27 million visitors were awed by the U.S. Census Bureau's exhibit.

The Census Bureau's exhibit was located inside the cavernous glass and faux-masonry U.S. Government Building alongside displays of U.S. currency, carrier pigeons, a live California redwood tree, and floor-to-ceiling fresh and saltwater fish tanks. As fairgoers watched, census clerks processed 1890 Census data using electric tabulating machines that had recently been invented by former Census Bureau employee Herman Hollerith.

Attendees were so impressed with the Census Bureau's exhibit and its innovative data-processing technology that fair organizers presented Herman Hollerith a bronze medal designed by sculptor Augustus Saint-Gaudens and U.S. Mint engraver Charles E. Barber.