I built this page when I found the first references to "Junior Muskrat Club" and "Natural Muskrat Club".  (I'd hoped there'd be a lot more.)

Detroit-area Lake Erie Metropark often hosts The Muskrat Club, a children's (K-3) event (especially during the summer).  Home page: The Huron-Clinton Metropolitan Authority Metroparks.  Wayne spring activities (June 8, 2000) and Metropark parties at 50 (June 9, 2000) from The Detroit News refer to this offering.

A few Bay City, Michigan, residents have banded together as the Muskrat Club.  They like to eat muskrat.  See Bay City club helps community, shares muskrat meals, The Detroit News, December 14, 2000.  Also mentioned in the February 12, 1999, Associated Press article "Lite-eating Muskrat" by Jim Suhr found on Animalnet Feb. 12, 1999 from Animalnet Archives, Department of Plant Agriculture, University of Guelph, Guelph, Ontario.

The Georgia Amateur Soccer Association apparently has a Muskrat Club.  See Muskrat Club from SoccerOnline.com.

For a $50 annual contribution to the Aldo Leopold Nature Center (Monona, Wisconsin), you'll be a "Muskrat Marcher".  Information is on their web page Become a true FRIEND of Nature!

For a $1000 contribution, you can become a Muskrat Rambler. See Friends & Supporters, Dauphin County Parks & Recreation from Dauphin County, Pennsylvania Parks & Recreation.

And then there is the fictional Muskrat Club, "where the young swells of St. Paul gather to drink and gamble".  It is mentioned in the book Sherlock Holmes and the Ice Palace Murders by Larry Millet, according to New Novels VII from New Adventures of Sherlock Holmes and RUSS-L list Recommendations - Holmes related from RUSS-L list Recommendations, The Hive.