Posen is a village in Cook County, Illinois, United States. Posen is the German-language name for the western Polish city of Poznań. The population of the village was 5,987 at the 2010 census, up from 4,730 in 2000.
Posen is located at 41°37′42″N 87°41′9″W (41.628234, -87.685723).
According to the 2010 census, Posen has a total area of 1.17 square miles (3.03 km2), all land.
The area that is now Posen was settled by farmers, mainly of Dutch and German origin, in the second half of the 19th century. In 1893 a Chicago-based real estate firm hired 75 agents in the Polish-speaking areas of Germany to sell land to Poles seeking to emigrate to the United States. Over the next few years the village emerged as a place largely inhabited by factory workers, mainly employed at nearby Harvey, who also had room on their lots for gardens. In 1894 the Roman Catholic Archdiocese of Chicago established a mission to serve the Polish residents of Posen, which was elevated to parish status as St. Stanislaus the Martyr in 1898.
In the 1930s the population of Posen was 98% of Polish origin, and in 1960 only 0.1% of the population was identified in the census as being not white, or 4 of the 4,513 inhabitants. In 1963 there were 7% black students that attended the Posen School.