The best time to go to Sullivan is typically during the late spring, summer, and early autumn months, from May through to October, when the weather is most pleasant for outdoor activities.Sullivan experiences warm, sunny weather during these months, with average temperatures in the mid-20s Celsius (70s Fahrenheit). This period is ideal for exploring the local parks, enjoying outdoor events, or visiting nearby Lake Shelbyville for water-based recreation.For those looking to attend the annual Little Theatre on the Square performances, the summer months are great as their main season runs from June to August. Booking in advance is recommended during this popular time.