Spring and autumn are the most comfortable seasons. April and May bring mild weather and the Lincoln sites are manageable before summer crowds arrive. September and October are similarly pleasant with good light for outdoor visits to Oak Ridge Cemetery and the State Capitol grounds.
Summer (June to August) is hot and humid, with temperatures regularly in the low 30s Celsius. The Lincoln Presidential Library is a good option on a hot afternoon — it is large, air-conditioned, and can absorb several hours. Winter is cold and grey, though all the major indoor sites remain open year-round. Springfield has no real high season for tourism; the Lincoln pilgrimage runs throughout the year and the city's attractions are rarely so crowded as to be a problem.