Waterloo was built on land that was part of a parcel of 675,000 acres (2,730 km2) assigned in 1784 to the Iroquois alliance that made up the League of Six Nations. Almost immediately—and with much controversy—the native groups began to sell some of the land. Between 1796 and 1798, 93,000 acres (380 km2) were sold through a Crown Grant to Richard Beasley, with the Six Nations Indians continuing to hold the mortgage on the lands.
The first wave of immigrants to the area was Mennonites from Pennsylvania. They bought deeds to land parcels from Beasley and began moving into the area in 1804. The following year, a group of 26 Mennonites pooled resources to purchase all of the unsold land from Beasley and discharge the mortgage held by the Six Nations Indians.
The Mennonites divided the land into smaller lots; two lots initially owned by Abraham Erb became the central core of Waterloo. Erb is often called the founder of Waterloo, as it was his sawmill (1808) and grist mill (1816) that became the focal point of the area.
In 1816, the new township was named after Waterloo, Belgium, the site of the Battle of Waterloo, which had ended the Napoleonic Wars in Europe. After that war, the area became a popular destination for German immigrants. By the 1840s, German settlers had overtaken the Mennonites as the dominant segment of the population. Many Germans settled in the small hamlet to the southeast of Waterloo. In their honour, the village was named Berlin in 1833 (renamed to Kitchener in 1916). Berlin was chosen as the site of the seat for the County of Waterloo in 1853.
Waterloo was incorporated as a village in 1857 and became the Town of Waterloo in 1876 and the City of Waterloo in 1948.