Many of the battle scenes were filmed on the actual battlefield site in Springfield, Missouri, by special permission of the National Parks Service.
During much of principle photography, the heat index exceeded 110 degrees; despite many extras clad in heavy, period correct uniforms, there were no instances of heat related illnesses.
The St. Louis massacre was filmed in the Rivermarket district of downtown Kansas City. It was chosen for its many surviving buildings from the period.
August Light was originally conceived as a 28 minute museum film for the Wilson's Creek National Battlefield. There was enough extra footage that the producers were able to create a feature nearly three times as long. It was only necessary to add one extra day of shooting, for the St. Louis Massacre sequence.
Principle photography began on the 146th anniversary of the battle, and the television premiere took place on the 150th.