The Investment Company Institute (ICI), an organization representing the mutual fund industry, and the Securities Industry Association (SIA) recently released the results of a survey of America's investors. It seems that word is getting out that the stock market is one of the best places, if not the best place, to grow your money in the long term. Let's review some of the findings.

First, half of all American households and a third of all individuals now own stock, directly and/or via mutual funds. That amounts to almost 57 million households. Pretty good, eh? True, but it still means that about half of Americans are letting this major wealth-building engine simply pass them by.

But more people in stocks is good. So what's been driving this movement into stocks? One major factor has been the rise of 401(k) plans at work, which typically offer employees many mutual funds to choose from. (Learn more about how to maximize your own plan in our 401(k) nook.) The ICI and SIA report that, "Between 1999 and 2005, the number of households owning equities through employer-sponsored plans, which often offer stock mutual funds as investment options, grew by 5.2 million, to 37.6 million." That's 16% growth in just six years.

As people get their toes wet with equities via retirement plans, many are also moving on to investing on their own, often through brokerages. This is good news for those who invest in brokerages -- such as Merrill Lynch (NYSE:MER), Motley Fool Stock Advisor pick Charles Schwab (NASDAQ:SCHW), E*Trade (NYSE:ET), Toronto-Dominion Bank's (NYSE:TD) TD Waterhouse, Ameritrade (NASDAQ:AMTD), and Morgan Stanley (NYSE:MWD). (Pop into our Broker Center for lots of guidance on how to find a better brokerage -- check out our handy comparison table there, too.)

"Americans clearly understand the benefits and value of investing in equities to reach their long-term financial goals," Frank Fernandez, SIA Senior Vice President, said in the survey. "Despite experiencing a market contraction that was one of the worst bear markets since the Great Depression, the number of individuals in the U.S. owning equities is up 5.2% since 2002, and up 14.4% since 1999." That's indeed promising, but I disagree that Americans are so stock-savvy. Just look at some stats from the recent Retirement Confidence Survey: Only 42% of surveyed workers have bothered to try to figure out how much money they will need in retirement. Of this subset that has tried, 35% consulted a financial advisor, 37% came up with its own estimate, and 10% "simply guessed!" Maybe the status quo has improved, but there's clearly a lot of room for improvement remaining.

Here's another interesting tidbit from the survey: ". Nearly three-quarters of all equity investors hold equities outside [retirement] plans. Professional financial advisers are the main conduit to equity ownership outside employer plans. More than three-quarters of investors who hold equities outside employer-sponsored plans in 2005 own equities purchased through advisers." This is good news only if the advisers are plunking them into good investments. I'm sure many are, but like any other profession, there are inevitably some duds out there among advisers. If you have an adviser, or are seeking one, drop by our Advisor Center, which can help you evaluate them better. (You might also consider trying our TMF Money Advisor financial planning service. It's inexpensive, offers personal, professional advice via phone, and you can try it for free.)

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Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article.