@PotomacBobYes it's true. It's still true but not to the same extent.
The Green Bay Packers are organized as a non-profit corporation.
Originally you had to be a resident of Green Bay, Wisconsin to own shares. This was written into the corporate by-laws.
I don't know the exact time line, but it was eventually expanded to any resident of Wisconsin and later the residency restriction was lifted completely.
The shares are not publicly traded and as far as I know, can only be sold back to the Green Bay Packers organization if you want to get rid of them.
I am a Wisconsin resident (not Green Bay) so I have some direct knowledge of this, but it's limited.
The info on this on Wikipedia ( https://en.wikipedia.org/wiki/Green_Bay_Packers,_Inc.#Stock_sales ) is accurate as far as I know.
One important thing, the NFL has a rule against corporate ownership of teams, however, the Packers have had this corporate structure since 1923 before the rule against corporate ownership was established so they have a grandfather clause exception to the rule.
There is one other team with an exception to the current franchise ownership rules.
The Houston Texans have an exception to a rule prohibiting franchise ownership by government entities (Harris County (where Houston is located) owns 5% of the team), again, it's a grandfather clause situation as the partial ownership of the team by the county predates the rule prohibiting ownership by government entities.