Peru is a city in LaSalle and Bureau counties, Illinois, United States. The population was 9,896 at the 2020 census, down from 10,295 at the 2010 census. It is part of the Ottawa, IL Micropolitan Statistical Area. Peru and its twin city, LaSalle, make up the core of Illinois Valley.

LaSalle County is located within the Fox Valley and Illinois River Valley regions of the U.S. state of Illinois. As of the 2020 Census, it had a population of 109,658. Its county seat and largest city is Ottawa. LaSalle County is part of the Ottawa, IL Micropolitan Statistical Area of Northern Illinois.