Sag Bridge, Illinois
Latitude and Longitude:
|Elevation||623 ft (190 m)|
|Time zone||UTC-6 ( CST)|
|• Summer ( DST)||UTC-5 ( CDT)|
Sag Bridge, Illinois is a populated place in southwestern Cook County, Illinois.  Sag Bridge is an important waterway junction between the Calumet Sag Channel and the Chicago Sanitary and Ship Canal. It is also the junction of IL 83 (Kingery Highway) and IL 171 (Archer Avenue) which meet at Sag Bridge to cross the Calumet Sag Channel together on the eponymous bridge. The community was named for a predecessor of the present bridge. It is within the village limits and postal delivery zone of Lemont, Illinois.
Other than the bridge for which it was named and the canal that the bridge crosses, the most significant feature of the community is the historic St. James at Sag Bridge Catholic Church, listed on the National Register of Historic Places.
Sag Bridge exists at a significant geophysical point, at the confluence of the Sag Outlet and DesPlaines Outlet from historic Lake Chicago, which joined at this point to form the Chicago Outlet River and eventually flow into the Illinois River and the Mississippi River. Those two outlets isolated a portion of the Valparaiso Moraine called Mount Forest Island, much of which has been preserved in its natural state as the Palos Division  of the Forest Preserve District of Cook County.
The high bluff of Mount Forest Island overlooking this critical location has served as a lookout for centuries. The French fort on the site was visited by Father Jacques Marquette on his journeys on the Des Plaines River several times in 1673. 
The community was settled by workers building the Illinois and Michigan Canal, who established their historic church in 1833. Rock quarries developed there in the mid-19th century due to the combination of an abundant supply of quality stone, and convenient transportation on the nearby canal. Though the quarries themselves no longer operate, businesses selling stone products continue in the Sag Bridge area today. 
Nothing remains of the original bridge at Sag Bridge, except for an isolated remnant of Old Archer Avenue leading to the south bank of its former site, which today provides access for fishing and hiking in the Sag Quarries  area of the Forest Preserve District of Cook County.
The most recent bridge at Sag Bridge was built in 1934, and carries both IL 83 and IL 171 across the Calumet Sag Channel. This classic, 4-lane Pennsylvania through truss bridge is still structurally sound today, however it is rated "Functionally obsolete" due to growing traffic volumes, especially at the congested awkward 5-way signalized intersection just south of the bridge where routes 83 and 171 diverge. 
- St. James at Sag Bridge Catholic Church
- Valparaiso Moraine
- Lake Chicago
- Illinois and Michigan Canal
- Calumet Sag Channel
- Chicago Sanitary and Ship Canal
- Site A/Plot M Disposal Site
- USGS description of Sag Bridge, Illinois, retrieved 2012-09-02
- Region 6 Map of Natural Areas & Activities (PDF) (Map). Forest Preserve District of Cook County. Archived from the original (PDF) on October 21, 2012. Retrieved May 26, 2012.
- Staff. "Parish History". Historic St. James at Sag Bridge. Retrieved 2012-09-16.
- "Chicago Brick and Stone Company". Retrieved 2012-09-16.
- Region 7 Map of Natural Areas & Activities (PDF) (Map). Forest Preserve District of Cook County. Retrieved 2012-09-16.
- "March 27, 1991 TORNADO". Lemont Area Historical Society and Museum. Retrieved 2012-09-16.
- Illinois Department of Transportation. "Bridge Information: Structure Number 160427". Archived from the original on 2014-01-16. Retrieved 2012-09-02.