Waterloo is the county seat of Black Hawk County, Iowa, United States. As of the 2000 census, the city had a total population of 68,747. It was the home of the Sullivan brothers, who were killed during World War II. It is the location of the Tractor Assembly Division & Product Engineering Center of Deere & Company. Waterloo is also the former location of Rath Packing. Due to its history of meatpacking the city is home to the National Cattle Congress.

Waterloo attracted a large African-American population because of meatpacking and other industries located in the city. In the 1980s Waterloo experienced some friction between the black community and the rest of the city. Many African-Americans in Waterloo reside on the east side of the city. In the 1990's a large influx of Bosnian war refugees were resettled by the federal government in Waterloo adding to racial tensions there. Around the same time, a new IBP packing plant attracted hundreds of Hispanics, adding to the racial equation.

Waterloo is home of the Waterloo Blackhawks, a team in the United States Hockey League which plays in Young Arena. It is also the home of the Waterloo Bucks, a summer collegiate league baseball team which plays in the Northwoods League. The team plays at Riverfront Stadium.

Waterloo was originally known as "Prairie Rapids Crossing". The town was built on top of a Native American village. The town is currently named after Waterloo, Belgium. The city's primary waterway is the Cedar River.