Waterloo is a town in Lauderdale County, Alabama, United States.

In 1880, when it first appeared on the U.S. Census, and again from 1910 to 1940, it was the second largest community in Lauderdale County after Florence, reaching its zenith of 524 residents in 1940.

It has since lost two-thirds of its population and since 1980, and ranks 8th and smallest of Lauderdale County's incorporated communities with 203 residents.

Second Creek, which flows from the north, empties into Pickwick Lake at Waterloo, creating a small inlet.

The point at which the states of Alabama, Mississippi, and Tennessee meet is located several miles northwest of Waterloo.

As of the 2020 United States census, there were 178 people, 68 households, and 43 families residing in the town.

Waterloo is in: The climate in this area is characterized by hot, humid summers and generally mild to cool winters.