It’s boom time again for the housing market in Nassau County, where prices have reached a new peak.

The median price for a closed home sale jumped to $505,000 last month in Nassau, 5.7 percent higher than a year earlier, the Multiple Listing Service of Long Island reported Thursday. The county’s previous record high of $502,500 came in 2007, at the height of the housing boom.

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In Suffolk County, home prices still lagged behind their pre-recession highs. The median price for a closed home sale in Suffolk was $365,000 in June, a 7.4 percent annual gain but still below the 2007 high point of $420,000, listing service figures show.

Soaring prices in New York City are pushing more buyers to Long Island, where they get into bidding wars for a scant supply of homes, said Gary Baumann, an associate broker with Douglas Elliman in Dix Hills and Port Washington.

“The demand from the city and the boroughs is just working its way out,” Baumann said.

Scarcity is giving sellers the upper hand, brokers said. The number of listings dropped last month by 15.6 percent year-over-year, to 12,879.

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Demand is strongest for homes asking up to about $500,000 in Suffolk and $750,000 in Nassau, Baumann said. The market for homes listed for more than $1 million is “a little bit softer,” he said.

The number of closed transactions fell by 3.5 percent in Suffolk and 3.3 percent in Nassau last month, compared with the same period a year ago. At that pace of sales, it would take 4.9 months in Suffolk and 4.3 months in Nassau to sell all homes listed for sale. A balanced real estate market has a six- to eight-month supply of homes, real estate brokers say.

In Suffolk, some homeowners want to sell, but they’re frustrated that Suffolk prices have not regained their previous peaks after falling in the recession, said Cynthia McKenna, managing broker at Keller Williams Realty in Hauppauge. As a result, she said, “they’re not even listing their homes.”

The last recession lasted from December 2007 to June 2009.

Baumann said the local economy appears to be strong enough to sustain the current rise in home prices, especially in Nassau, where residents can commute to high-paying jobs in Manhattan.

However, he said, one cautionary note is that many homeowners have adjustable-rate mortgages and little or no equity in their properties.

In an indication that current home shoppers may be gravitating to Suffolk’s more affordable housing market, the number of contract signings increased year-over-year by 7.5 percent in Suffolk and 0.5 percent in Nassau last month.

McKenna said she is “not celebrating” the price gains since she believes they’re driven primarily by scarce supply, rather than real gains in Long Islanders’ incomes and buying power.

“We really need more income, and that’s not something we can fix,” McKenna said.