Illinois History of Alexander, Union and Pulaski Counties, Illinois   http://www.findagrave.com/cgi-bin/fg.cgi?page=csr&CScnty=780&CSsr=21& Union County, Illinois Graveyards http://landplats.ilsos.net/Union.html Union County, Illinois platmaps http://en.wikipedia.org/wiki/Union_County,_Illinois Union County is a county located in the U.S. state of Illinois . According to the 2010 census , it has a population of 17,808, which is a decrease of