Crab Orchard is an unincorporated census-designated place east of Marion in Williamson County, Illinois, located along an old route of Illinois Route 13 now parts of that is Crab Orchard Road and East that is now Ranch Ln it's South of where the Illinois Route 13 is. The upper branches of Crab Orchard Creek which eventually feed into Crab Orchard Lake flow nearby and gave the community its name. For a brief time during the US Civil War, it was known as Erwinsville, which is the name in the original plat of the village. In its early days, it had the nickname "Steal-Easy." The Crab Orchard post office was established 18 August 1853 and discontinued operations 15 May 1924. It's now served by the Marion post office. As of the 2010 census, Crab Orchard has a population of 333. Crab Orchard has an area of 1.430 square miles (3.70 km2); 1.395 square miles (3.61 km2) of this is land, and 0.035 square miles (0.091 km2) is water.