Indigenous peoples settled in the area at least 3,000 years ago, and a few of these groups to settle in the area included Woodland Natives, Iroquois, and Mississaugas.
European contact first occurred in the early 1600s. In 1615, Samuel de Champlain traveled through the area and briefly stayed near the present-day site of Bridgenorth, just north of Peterborough.
The county was founded as the District of Colborne in 1838, centred on Peterborough, which became the County of Peterborough in 1850. In 1862, the County was re-divided into Haliburton County, Peterborough County, and Victoria County (now the City of Kawartha Lakes).
The centre of the County was originally the courthouse, which is still considered an important historical site. The county was named in honor of Col. Peter Robinson, who brought 2,000 settlers from Ireland in 1825.