In terms of precipitation, rainfall in Marion, Illinois ranges from 3.1 - 4.9 inches per month. May is typically the wettest month, when rainfall can reach 4.9 in. September is typically the driest time to visit Marion, Illinois when rainfall is around 3.1 in.
If weather is an important factor for your trip to Marion, Illinois, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 78.8 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 33.8 F).