Most investors are aware of the market's dividend behemoths, such as Procter & Gamble and 3M, which have been consistently paying and increasing their dividend payouts for 56 and 54 years, respectively.

However, there a few companies that have a longer payout history than these dividend giants. Currently, two of these dividend old-timers offer yields that exceed 4%.

The company with the longest dividend history is Diebold (NYSE:DBD), which has been consistently paying and increasing its dividend for 60 years. Coming in second is American States Water (NYSE:AWR), which currently has a yield of 2.9%, with a payout history stretching back 58 years. In third place is Dover (NYSE:DOV), with the lowest yield in the group at 1.7% and a payout history of 57 years. Dover has the same payout history as Northwest Natural Gas (NYSE:NWN), which offers a yield of 4.2%. Interestingly, all of these companies (excluding Dover) have a market capitalization of less than $2 billion. It appears that in this case, smaller is better.

What's the reason behind the payout history?
If there's one thing all that all four of these companies have in common, it's age -- and with age comes experience. In particular, both Diebold and Northwest have more than 150 years of history behind them. American States first came into existence back in 1929, when the company acquired its first water systems. Dover is only a baby in comparison, but as the largest of the four companies, its size makes up for its lack of experience.

So how have these companies been able to consistently pay a dividend for more than half a century? For a start, American States provides an essential service to more than 1 million people throughout California and portions of Arizona. The company is a holding company with many smaller utility subsidiaries under its umbrella. Many of the services that American States provides are high-margin, and as such the company is highly cash-generative and reported a gross margin of 84% for fiscal 2012.

Northwest Natural Gas operates similarly. As a provider of natural gas to more than 686,000 homes and businesses within 107 communities in Oregon and Southwest Washington, the company has a certain amount of pricing power. This allows it to achieve high profit margins. Moreover, thanks to the sliding price of natural gas during the past five years, the company has seen its gross margin nearly double from 34% to 51%. Depreciation costs have hit its net income, however, so the company's net margin stood at 8.2% for fiscal 2012. This is still 0.8% higher than the net margin reported during 2009, though.

What's more, it appears that Northwest is loved by its customers, as the company has ranked highest among the Western U.S. large utilities for customer satisfaction in the J.D. Power Gas Utility Residential Customer Satisfaction Study for three out of the past six years.

Diebold's specializes in locks, safes, and security. The company made a name for itself back in 1871 when the Great Chicago Fire destroyed everything within a four-mile radius except for 878 Diebold safes, which remained intact. Diebold is now in charge of protecting such items as the U.S. Constitution, the Bill of Rights, and the Declaration of Independence. The company is also a leader in its field for ATM production and design.

Will these payouts continue?
With each company notching up more than half a century's worth of payout history, how much longer will these payouts last? In the case of Northwest, I would say the company has plenty of room for another 50-plus years of payout growth. During fiscal 2012, the company's cumulative dividend payout of $48 million for the whole year was covered more than three times by the company's operating cash flow of $169 million. American States is also easily able to cover its cumulative annual dividend payout of $24 million, as it reported an operating cash flow of $101 million for fiscal 2012.

Unfortunately, Diebold's payout could come under some pressure in the near future. During fiscal 2012, the company's cumulative dividend payout of $73 million was less than two times covered by its operating cash flow of $135 million. What's more, Diebold's operating cash flow has been falling consistently since 2009 from a high of just less than $300 million to the current figure of $135 million. That makes Diebold one to watch for the moment.

Dover, on the other hand, was easily able to cover its cumulative $184 million dividend payout during 2012 with an operating cash flow of $730 million. The company also brought back $400 million worth of stock during the period.

Foolish summary
In some cases, past performance is a good indicator of future returns. Based on the dividend history of these four companies, I believe they will be able to maintain their dividend payouts for many years to come. Indeed, all four companies have good reputations, and their cumulative dividend payouts are generally well-covered by free cash flow.

If you're looking for dividend security for many years to come, these companies could be your best choice.

Fool contributor Rupert Hargreaves has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.