To join a credit union, you will need to check the credit union’s membership criteria and then — if eligible — apply online, in-person or over the phone, depending on the credit union. In many cases, membership is restricted to people who live in a certain area or work for a certain employer. That being said, the list above provides you with an array of credit unions that allow you to join simply by making a small donation or joining a partner organization.

Source: https://www.magnifymoney.com/blog/best-of/credit-unions-anyone-can-join/