Peru is a city in LaSalle County, Illinois, United States. The population was 10,295 at the 2010 census. It is part of the Ottawa–Streator Micropolitan Statistical Area. Peru and its twin city, LaSalle, make up the core of the Illinois Valley.
Peru is located at 41°20′4″N 89°7′39″W / 41.33444°N 89.1275°W / 41.33444; -89.1275 (41.334458, -89.127385).
According to the United States Census Bureau, the city has a total area of 6.1 square miles (15.7 km²), of which, 5.9 square miles (15.4 km²) of it is land and 0.1 square miles (0.3 km²) of it (1.82%) is water.