The Chicago Historic Resources Survey was a decade-long effort to catalog buildings of important architectural or historic significance constructed in the city prior to 1940. Completed in 1995, the survey is the frontline resource for city planners and preservationists to determine which buildings immediately merit close attention.

The highest designation, "Red," is reserved for buildings deemed to have importance either historically or architecturally for the entire city, state of country. There are about 300 such buildings in the city. The second highest designation, "Orange," represents a much larger selection of buildings, numbering just under 10,000 across the city. Whenever an owner or developer seeks a permit to demolish or significantly alter an "Orange-rated" building, it automatically triggers a 90-day "hold" while the building is evaluated by city staff to see if it qualifies for landmark protection or if neighbors or preservationists can provide an alternative. Still, dozens of Orange-rated buildings are demolished each year.

With the current development cycle in full swing, many historic buildings around the city are endangered of being demolished to make way for new projects, or in being so altered as to lose any historic character. These are just some of the most-endangered of that cohort of buildings.