By S. MITRA KALITA

Sales in many vacation communities across the U.S. soared last year to levels not seen since boom times, driven by deep discounts, cash purchases and buyers’ rising stock portfolios.

On Mercer Island, Wash., waterfront sales nearly tripled in 2010, compared with a year earlier, reaching par with 2006 volume there. Sales on Hilton Head Island, S.C., rose 14% for the year. Palm Beach, Fla., experienced a 40% annual increase and a 54% increase in homes under contract, indicating an especially strong fourth quarter. Palm Beach sales volume now is comparable to its 2007 peak. These figures were gleaned by brokers in each locale.

“The proverbial train has left the station,” said Ned Monell, an agent with Sotheby’s International Realty in Palm Beach. “We haven’t felt energy like this in a long time. Buyers sense that they’ve been on the sidelines long enough.”

The question now is whether the momentum will last. The strength of second-home sales paints a stark contrast to the overall housing market, which is expected to worsen in 2011.

Existing-home sales in November rose 5.6% on an annualized basis, according to the National Association of Realtors, a trade and lobbying group. Last month, the Case-Shiller housing index of 20 cities showed prices across the U.S. fell in October, and most analysts predict another 5% to 10% slide in the coming year.

Data for the nationwide vacation-home market aren’t tracked regularly. The National Association of Realtors conducts an annual survey of home buyers, but results for 2010 won’t be out till March.

Yet the market for vacation homes, based on local sales data, appears to be booming. The comeback, NAR economist Lawrence Yun said, has been helped by gains in the stock market and an improving economy, which have made wealthier Americans more upbeat about the future. “It also implies that prices in some markets have come down so much that people are fighting for those properties,” said Mr. Yun, noting that demand is strongest in areas close to stable labor markets.

According to the NAR, one in 10 real-estate transactions in 2009 was for the purchase of a vacation home. And though a small fraction of the overall market, it is significant because vacation homes are often big-ticket properties and attract discretionary buyers. Just four houses sold last year on Madeline Island, Wis., for example, but the island’s average dwelling sells at two to three times the price of the county average, said Eric Kodner, a realty broker on the island.

Sales of second homes are showing an uptick even in more-affordable communities. In some locations, prices are even inching upward. Cape Cod sales climbed nearly 9% in 2010 from 2009, while prices rose 7%. Monroe County, Pa., in the heart of the Pocono Mountains, saw a 3% decline in transactions, but its Lake Naomi resort community was up nearly 15%. A one-acre plot off Lake Naomi recently fetched $1.1 million, a record deal for the area.

Still, in most markets where demand has improved, prices haven’t. For Realtor Andy Twisdale in Hilton Head, S.C., it is too soon to rejoice; prices are down almost a third over the past five years. “People are buying at the very low end of the product,” he said. “The financing is very difficult. Banks are requiring 25% down and crystal clean credit.”

Buyers who qualify or can pay cash say this is the time to take the plunge. On New Year’s Day, the Makarewicz family arrived in Pocono Pines, Pa., to look for a vacation home. They already own their primary residence in northern New Jersey and own a property in Damascus, a northeastern Pennsylvania town along the Delaware River. But the family says the latter doesn’t offer enough things to do: Not enough shopping. Not enough activities for kids. Not even enough fish.

“How’s the bass here?” Joe Makarewicz, a vice president for sales at a financial-services firm, asked Re/Max Realtor Rob Baxter as the two looked at floor plans.

The family plans to sell the Damascus house, which would allow them to pay cash for one near Lake Naomi. The resort community at Lake Naomi boasts pools, tennis courts, a recreation center and a golf course—and is equidistant from New York and Philadelphia.

Some second homes had been stuck on the market because sellers wouldn’t budge on price; unlike owners of primary homes, they often aren’t in a hurry to move.

“Sellers have become aware that they have to price their homes accordingly,” said Harald Grant, a senior vice president at Sotheby’s in New York’s ritzy Hamptons region. “There’s a perk in the market because a lot of prices have come down to where they should be.”

This shift became clear to K. David Hirschey, who runs a consulting business in Minneapolis, as he hunted for a home on Madeline Island.

After competing in a summer swimming competition on the island, Mr. Hirschey decided to buy a home there, perhaps to rent it a few years and maybe retire there eventually. The first offer he made was rejected, he recalled, because the seller said, “We don’t negotiate on properties here.” The same thing happened with his bid on the next house.

Then he found a third property—four bedrooms, three baths—that began as a sale by owner, was taken off the market, then relisted under one broker, then another. It had been initially priced at $1.25 million, and remained on sale for two years.

“When I saw it, it was listed at $687,000,” said Mr. Hirschey, a father of four children. He offered $530,000, furnishings included. “They wanted to negotiate and I said no,” he said.

The tactic—an all-cash offer—worked, and Mr. Hirschey closed on the house in November, just in time for his family to spend the holidays there.