In the early ’70s, four satiated but dissatisfied couples on their way home to Minnesota from a social event in a distant state reignited a conversation they’d been having about their gripe. Having to pack up and travel to meet like-minded people was a big bother. Surely there was a way to meet more people like them close to home. Other swingers.

So they made a plan. If they combined efforts, they thought, they could start their own swingers club and create a scene right in their own town. They could swing more often and with more people. These couples called themselves the Executive Committee of their new outfit. They didn’t yet suspect what it would be like to herd swingers and guard their privacy.

The group they started, the Silver Chain Social Club, brought to life the hopeful vision of its eight founders, along with a grave concern for the secrecy of its conventional-seeming, suburban members. Club activities—events like bowling dates, costume parties, panel discussions, and support groups—were for socializing only, and members were supposed to swap partners and have sex on their own time. (“We wanted the club to operate on a high plane—first class always,” a founder reminisced.) The founders hoped that members could quietly recognize each other in public by displaying the jewelry that gave the club its name. The Executive Committee really wanted those trademark silver chains to have “77” pendants—honoring a favorite sexual position (69) plus eight (ate) more. (Get it?)—but the plan fell through. “Our efforts to find a manufacturer at a reasonable cost have been fruitless,” ended the dream.

I know this much about the Silver Chain’s meetings, hundreds of members, and guiding principles because these materials, which span from 1974 to 1978, are available for viewing in the sedate, high-ceilinged reading room of the Minnesota Historical Society. Two members preserved by-laws, newsletters, correspondence, and, perhaps dangerously, dating-app-esque profiles (with a first name but only a last initial). In the early 1990s, the records were found in a safe deposit box at First Bloomington Lake National Bank, and the papers made their way to the state’s historical agency via a Minnesota law that gives the Society first claim to abandoned historic materials. They may be the only such records preserved anywhere in the world in a historical archive, and they give a rare look into the sometimes mundane, often unexpected workings of a swingers club just trying to keep track of its sexy ongoings.

The early ’70s were free love, suburban suffocation, and feminism on the rise. All over America, people were reexamining relationships and marriage. Swinging might have spun out of the organized partner swapping of U.S. military pilots who flew in World War II and the Korean Conflict. It blossomed during the decade along with communal living, gay liberation, and extra-legal domestic partnerships—all attempts to break the numbing shackles of button-down lifestyles. Studies from the era (most flawed and unreliable, to be fair) put the number of swingers in the American population at 2 to 4 percent, but only a small number of them tried to take on the role of a sexual community board to organize fellow believers.

By 1974, the Silver Chain’s Executive Committee had drawn up a playful set of rules and regulations that laid out the club’s purpose: to allow members to meet, mingle, and share “general good times.” Couples over 21 could join by invitation only with the good word of an established member who could vouch for their dedication to swinging. No spectators allowed. No single members, either. While many “straight” people—that’s swinger parlance for “non-swingers”—imagined “wife swapping” (as it was then sometimes called) as a sordid, hormone-charged activity for perverts, Silver Chain members went out of their way to emphasize courtesy and deference in their relationships. It was swinging infused with Minnesota Nice.