The Calumet Astronomical Society was founded in the summer of 1975 at the Hammond Public Library. There were initially about 20 members, many of whom had made their own telescopes at the Adler Planetarium's Optical Shop. Meetings soon moved to the Griffith Public Library with monthly group observing sessions at Stony Run County Park in Leroy. During the late 1980's CAS constructed a small roll off roof observatory at Birdland, a private arboretum near Lake Village.
CAS continued as a small social organization until 1990, when under the leadership of Steve Miller, it moved its observing site to Lemon Lake County Park in Crown Point and began public outing observing sessions. These were continued through the 1990s, drawing much public attention. Additional public events were held during the late 1990's at Indiana Dunes State Park, Indiana Dunes National Lakeshore, Deep River County Park, Deep River Water Park, Sunset Hill Farm County Park, Taltree Arboretum, and Oak Ridge Prairie County Park. Partnerships were entered into with NIAG, the Northern Indiana Astronomical Group, and the Indiana Family Star Party sponsored by the Wabash Valley Astronomical Society. Throughout this period, meetings were held at the Munster Public Library.
In 2000, CAS incorporated as an IRS 501c3 not for profit public benefit corporation. A board of directors was formed and handled business separate from the Society general meetings.
In 2000, CAS also became involved in what became the Conway Observatory project. This led to the observatory's installation south of Buckley Homestead County Park in Lowell during the summer of 2005 and the establishment of the Calumet Astronomy Center on this property.
Today the Society is a fellowship of approximately 100 amateur astronomers and astronomy enthusiasts that contribute to the Society's public outreach mission and pursue their own goals in astronomy. Active partnerships with the Lake County Parks and Recreation, and Purdue Calumet University result in superior public programs and facilities. CAS is the most active amateur astronomy organization in the Chicago area. Meeting are held at the Merrillville Community Planetarium in Merrillville, Indiana.