Ten interstate compacts:
- Great Lakes Commission (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin)
- Delaware River Port Authority (Pennsylvania and New Jersey)
- Washington Metropolitan Area Transportation Authority (Maryland, Virginia, and Washington, D.C.)
- Education Commission of the States (all States except Washington, three territories, and Washington, D.C.)
- Colorado River Compact (Colorado, New Mexico, Utah Wyoming, Nevada, Arizona, and California)
- Pacific States Marine Fisheries Commission (California, Oregon, Washington, Idaho, and Alaska)
- Delaware River and Bay Authority (Delaware and New Jersey)
- Atlantic States Marine Fisheries Commission (Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, and Florida)
- Bi-State Development Agency (Missouri and Illinois)
- Tahoe Regional Planning Agency (California and Nevada)
An interstate compact is a legally binding, Congressionally authorized agreement between two or more states. The "Congressionally authorized" part is important, because the U. S. Constitution states that "no state shall enter into an agreement or compact with another state" without the consent of Congress. Without Congressional approval, it's just words on paper.
I wonder why Washington withdrew from the Education Commission of the States?