Pike County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 16,430, which is a decrease of 5.5% from 17,384 in 2000. Its county seat is Pittsfield.
Pike County was formed on January 31, 1821 out of Madison County. It was named in honor of Zebulon Pike, leader of the Pike expedition in 1806 to map out the south and west portions of the Louisiana Purchase. Pike served at the Battle of Tippecanoe, and was killed in 1813 in the War of 1812.
Prior to the coming of the first European settler to Pike County, French traders, hunters, and travelers passed through the native forests and prairies. Originally Pike County began on the south junction of the Illinois and Mississippi rivers. The east boundary was the Illinois River north to the Kankakee River to the Indiana State line on north to Wisconsin territorial line and then west to the Mississippi River to the original point at the south end. The first county seat was Cole's Grove, a post town, in what later became Calhoun County. The Gazetteer of Illinois and Missouri, published in 1822, mentioned Chicago as "a village of Pike County" containing 12 or 15 houses and about 60 or 70 inhabitants.
The New Philadelphia Town Site was listed on the National Register of Historic Places in 2005 and designated a National Historic Landmark in 2009. It was the first town founded by an African American before the American Civil War. Frank McWorter was an early free black settler in Pike County. He had invested in land there sight unseen after purchasing the first few members of his family out of slavery. In 1836 he founded the town of New Philadelphia, near Barry, Illinois. He was elected mayor and lived there the rest of his life. With the sale of land, he made enough money to purchase the freedom of his children. After the railroad bypassed the town, its growth slowed and it was eventually abandoned in the 20th century. The town site is now an archaeological dig.