In May 1999, the eastern massasauga was added to the list of candidate species.  Candidate species are those considered for possible addition to the list of Federal Endangered or Threatened species.  The Candidate Conservation Agreement was developed to expedite implementation of conservation measures for the eastern massasauga as a collaborative and cooperative effort between the Cook County Forest Preserve District, the Illinois Department of Natural Resources and the U.S. Fish and Wildlife Service.

This is the second Candidate Conservation Agreement that the Chicago Illinois Field Office has been able to secure.  In March 2005, the Chicago office secured a Candidate Conservation Agreement with the Lake County (Illinois) Forest Preserve District and the Illinois Department of Natural Resources which addresses the management needs for the northern most population in Illinois.  The agreement with Cook County extends southward and addresses threats for four more populations that may serve as a link to the southernmost populations in Will County, Illinois.  The Chicago office is continuing this Northeastern Illinois effort to conserve the eastern massasauga rattlesnake by pursuing a Candidate Conservation Agreement with the Forest Preserve District of Will County.  In addition, the Chicago Illinois Field Office is partnering with the Illinois Department of Natural Resources to develop a statewide recovery plan for the eastern massasauga.