From Opus

The Great Lakes Area as used in Opus is a term that refer to all or some of those states that border the Great Lakes in the USA and Canada:

• Minnesota
• Wisconsin
• Illinois
• Indiana
• Michigan
• Ohio
• Ontario (in Canada)

• Pennsylvania
• New York

The latter two are often excluded from this group.

In a few cases, the lakes themselves may be what the link intends: these are Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario.