Onarga is a community located in the U.S. state of Illinois. It is within Iroquois County and founded in 1854. It has a total area of 1.18 square miles at 40°42′54″N 88°00′22″W. The elevation is 669 feet above sea level. As of the 2010 census data, it had a total population of 1,368. The population density was 1,104.15/sq mi. Estimated per capita income in 2016 was $22,069. It has Zip code 60955.