Credit unions have been around for quite a while but it hasn't been until the last few years, after people have grown wise to the excesses of the "too big to fail" commercial banks, that they've really grown in popularity. The first "bank" I joined was a credit union, Teachers Federal Credit Union, and I kept that account until just a few years ago. It's my firm belief that everyone should have an account at a credit union because they represent everything good about banking.
Here's the biggest difference between credit unions and commercial banks—credit unions work for you, banks work for their shareholders. Commercial banks, especially those that are publicly traded, are obligated to act in the best interests of its shareholders. Credit unions are also obligated to act in the best interests of their shareholders. The difference is that the shareholders of a credit union are its customers.
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It's the reason why your checking account is called a "share draft" account, rather than a "checking" account. This is also why interest rates on deposit accounts is usually higher at a credit union (and why loan interest rates are lower). There are plenty of reasons why credit unions are better than commercial banks, here are just a few:
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There are downsides to credit unions, it's not all perfect. Credit unions, by law, have to restrict membership in some way. This is usually done by membership to an organization, such as limiting membership to military and their families, or by geographic area, such as a city or county. Another downside is that credit unions, since they are very small, will have a limited geographic footprint and thus you may be required to travel a ways to get to a branch or ATM. Some credit unions partner with ATM networks to alleviate this, so check with the credit union.
In the end, all of the hassles are worth it. Credit unions are a fantastic way to bite your thumb at the "too big to fail" banks. If you've been searching for a way to sever your ties to a commercial bank, consider credit unions.