Dividend stocks have become increasingly important to investors, and companies are taking note.

Some 84% of S&P 500 Index components were paying dividends as of April 30, according to FactSet.

Except for a slight dip during the 2008 financial crisis, the number of S&P 500 companies that pay dividends has been rising for the last decade. Last month's tally represented the highest month-end figure in 18 years.

Dividend-paying stocks are particularly appealing amid today's market volatility and low interest rate environment. Indeed, companies that paid dividends outperformed nonpayers this past March and April - both rocky months for stocks. Returns in March and April averaged 1.3% and 0.89% respectively for dividend payers, compared with negative 2.3% and negative 2.6% respectively for nonpayers, FactSet reports.

Last week, 72 companies hiked their payouts. Following are 25 notable dividend stocks that boosted payouts in the week ending May 9.

Access Midstream Partners LP (NYSE: ACMP) increased its quarterly dividend 50% to $0.09 per share for a yield just shy of 4%.

Baxter Intl. Inc. (NYSE: BAX) boosted its quarterly dividend $0.03 to $0.52 a share for a 2.77% yield. The new rate maintains Baxter's dividend payout ratio of approximately 40%. Since 2008, the healthcare giant has more than doubled its dividend.

Buckeye Partners LP (NYSE: BPL) raised its quarterly dividend 1.1% to $1.10 a share for a 5.73% yield.

Cabot Corp. (NYSE: CBT) increased its quarterly payout $0.02 to $0.22 a share for a 1.37% yield.

Cardinal Health Inc. (NYSE: CAH) upped its quarterly dividend 13.2% to $0.34 a share for a 2.13% yield.

Portfolio Strategy Alert: Over time you can make more money in dividends than you paid to buy the stocks that produce them. Get today's best dividend strategy for building wealth in the low-yield era.

Chesapeake Utilities Corp. (NYSE: CPK) raised its quarterly dividend 5.2% to $0.40 a share for a 2.54% yield. The Dover, Del.-based company has maintained or hiked its dividend for 53 straight years.

FactSet Research Systems Inc. (NYSE: FDS) fattened its quarterly dividend $0.04 to $0.39 a share for a 1.48% yield.

Hyster-Yale Materials Handling Inc. (NYSE: HY) hiked its quarterly payout 10% to $0.25 a share for a 1.25% yield.

J2 Global Inc. (Nasdaq: JCOM) boosted its quarterly payout 2.9% to $0.27 a share for a 2.24% yield.

Microchip Technology Inc. (Nasdaq: MCHP) moved its dividend up 0.1% to $0.355 a share for a 3.03% yield. The dividend increase followed record Q4 and fiscal 2014 revenues and earnings. The semi-conductor earned $0.50 per share, or $111.5 million, in Q4 2014, up 88% year over year.

Nacco Industries Inc. (NYSE: NC) raised its dividend 3% to $0.2575 a share for a near 2% yield.

Nielsen Hldg N.V. (NYSE: NLSN) increased its quarterly dividend a nickel to $0.25 a share for a 2.13% yield.

Penske Automotive Group Inc. (NYSE: PAG) hiked its quarterly dividend a penny to $0.19 a share for a 1.66% yield. "The increase in the dividend reflects the continued confidence we have in the strength of the auto retail market and our ability to continue to grow our overall business," a company statement said.

PepsiCo Inc. (NYSE: PEP) sweetened its quarterly dividend 15.4% to $0.655 a share for a 3.01% yield. It's the snack and beverage behemoth's 42nd consecutive annual dividend enhancement. Additionally, Pepsi plans to increase stock repurchases in 2014 to $5 billion. The two programs combined are expected to return a total of $8.7 billion to shareholders this year, a 35% increase from 2013 levels.

Phillips 66 (NYSE: PSX) hiked its quarterly dividend 28.2% to $0.50 a share for a 2.44% yield. It's the company's second increase in 6 months.

Just-released: Of the almost 5,000 dividend-paying stocks to choose from, these three companies provide superior payouts and superior long-term growth potential.

Quaker Chemical Corp. (NYSE: KWR) increased its quarterly payout a nickel to $0.30 a share for a 1.60% yield. It's the Conshohocken, Pa.-based company's 39th dividend enrichment in 42 consecutive years of paying dividends.

Sabra Healthcare REIT Inc. (Nasdaq: SBRA) raised its quarterly dividend $0.02 to $0.38 a share for a 5.33% yield.

Salient MLP & Energy Infrastructure (NYSE: SMF) raised its quarterly dividend 0.9% to $0.353 a share for a 6% yield.

Semgroup Corp. (NYSE: SEMG) upped its quarterly dividend $0.02 to $0.24 a share for a 1.36% yield.

Spectra Energy Partners LP (NYSE: SEP) increased its quarterly dividend 1.8% to $0.55 per share for a 4.24% yield.

Telus Corp. (NYSE: TU) raised its quarterly payout 5.6% to $0.34 a share for a 3.86% yield.

Terra Nitrogen Co. LP (NYSE: TNH) hiked its quarterly payout $1.00, or 43.3%, to $3.01 a share for a 7.33% yield.

USA Compression Partners LP (NYSE: USAC) upped its quarterly distribution 2.1% to $0.49 a share for a 7.26% yield.

Westpac Banking Corp. ADR (NYSE ADR: WBK) boosted its semi-annual payout 7.5% to $0.83 a share for a near 5% yield.

Whiting USA Trust II (NYSE: WHZ) increased its quarterly dividend 3% to $0.67 a share for a 21.47% yield.

Today's Top Story: If you own gold, or are thinking of buying some, here's something you need to consider: Not all gold is created equal. Here's what to know before you buy...