The Sigma Alpha Iota Decatur Alumane Chapter was chartered in Decatur, Illinois, on October 8, 1938. Millikin University, a private school then affiliated with the Presbyterian Church, is located in Decatur. It has an award-winning School of Music with Nu Chapter, an SAI Collegiate Chapter. Nu Chapter graduates, who lived in the Decatur area, formed the Decatur Alumnae Chapter. Esther Requarth, Nu Chapter member and then a member of the Alumnae Chapter, wrote the Sigma Alpha Iota Symphony.
The Decatur Alumnae Chapter has had a continuous history of being an active presence in the Decatur Area. It has had close ties with Millikin's Nu Chapter. The Decatur Alumnae Chapter holds auditions for several Alumnae awards for Nu Chapter. The recipients perform at the annual Rose Tea hosted by the Alumnae Chapter.