Anna State Hospital (later C.L. Choate Mental Health and Developmental Center) – Ruhe1986, Public domain – Wikimedia Commons Anna is located in Union County. About 4,303 people live here (as of 2020). Between 2010 and 2020, the population declined from 4,442 to 4,303. The region is at 190 meters above sea level. The area covers about 9.3 square kilometers. There are about 164 streets in Anna. The region was founded in 1854. The postal codes are 62906. The dialing code is 618. Anna is city in Union County, Illinois, United States. Among other things, Anna has hotels and schools. More information at cityofanna.org.