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.
Located on the Illinois River, Peru lies 3 miles west of the intersection of two major interstate highways: Interstate 39 and Interstate 80. The city is also near the western terminus of the historic Illinois and Michigan Canal. Starved Rock State Park, a regional tourist attraction, is located 5 miles south-east of the community. Peru has a twin city on its eastern edge, LaSalle.
The city was organized as a borough in 1838, and was officially incorporated as a city on March 13, 1851.
The city is the birthplace and hometown of world renowned violinist Maud Powell, who was born on 1112 Bluff Street, where the 251 bridge currently stands. The city was home to Turn Hall, which was the location of Maud Powell's first performance.
The city was also the world headquarters of Westclox clock company. When Westclox closed, in the late 1970s, the population fell. The city is also the headquarters for Maze Lumber and Maze Nails - founded in 1848. The city was also home to Star Union Brewery, which closed in 1963 when it was bought out by Canadian Ace. The city also was home to James Barton, the inventor of the polygon mill, which stood in the north eastern section of town between 12 street, and Pulaski. Barton's home, which was called by local residents the "castle" due to its stone central turret, was adjacent to the mill, and still stands today.
Home of the world-famous circus performer, Scott Lungwitz, who was killed in a tragic horse diving accident.
In recent years, Peru has evolved into a regional commercial center, boasting a 50-store shopping mall (the largest within 55 miles) as well as several other national retailers. The area has also enjoyed the arrival of several small industrial/manufacturing firms. The completion of Interstate 39 in the early 1990s helped foster much of this new growth, making the city especially attractive to prospective distribution centers.
Peru is home to the offices of Carus Chemical Company, the largest manufacturer of potassium permanganate in the world. Maze Nail, one of America's last nail makers - proudly producing 100% American made nails is located in Peru, Illinois as well. Started in 1848, it is also one of the oldest continuously operating businesses in Peru.
Peru is also home to the national headquarters of American Nickeloid.
There were 4,143 households out of which 27.3% had children under the age of 18 living with them, 53.7% were married couples living together, 7.9% had a female householder with no husband present, and 35.5% were non-families. 31.5% of all households were made up of individuals and 15.5% had someone living alone who was 65 years of age or older. The average household size was 2.33 and the average family size was 2.93.
In the city the population was spread out with 22.0% under the age of 18, 7.5% from 18 to 24, 27.3% from 25 to 44, 21.9% from 45 to 64, and 21.4% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 89.8 males. For every 100 females age 18 and over, there were 87.9 males.
The median income for a household in the city was $37,060, and the median income for a family was $48,180. Males had a median income of $39,722 versus $21,961 for females. The per capita income for the city was $20,658. About 4.8% of families and 7.5% of the population were below the poverty line, including 12.8% of those under age 18 and 4.7% of those age 65 or over.