Even as more “for sale” signs popped up Long Island yards last month, brisk sales meant fewer were available compared to a year earlier, a report released Thursday said.

Confidence in the improving housing market drove new listings in Nassau County up 8.6 percent to 2,068 in May and up 5.7 percent in Suffolk to 2,342, according to the New York State Association of Realtors Inc.

At the same time, buyers have been getting off the sidelines, closing deals and pushing the number of homes for sale down 20.3 percent in Nassau to 7,655 and down 14.4 percent to 10,789 in Suffolk.

“The supply coming onto the market can’t keep pace with demand,” said Jonathan Miller, president and chief executive of appraisal firm Miller Samuel Inc.

Statewide, the association’s data show new listings are up 7.3 percent and inventory is down 15.9 percent.

“There’s been a strong buyer demand with a declining supply in available inventory,” said association spokesman Salvatore Prividera Jr., speaking about the New York market generally.

Though falling, a measure known as the months supply — the number of months it takes to sell all inventory at the current pace of sales — is still greater than what it was in a more robust market before the housing crash.

“Six to six-and-half months supply is considered to be a balanced market,” he said.

In May, Nassau had 8.7 months supply and Suffolk had 11.3 months supply.

Long Island lagged behind the nation in price increases in May. Across the nation median sales prices rose 15.4 percent to $208,000 compared to a year earlier, according to the National Association of Realtors. Nassau prices were unchanged at $390,000 and Suffolk prices rose slightly to $315,000, a 3.7 percent increase.

Nonetheless, Long Island’s improving picture is heading the same direction as the rest of the country. Year over year closed sales in Nassau improved slightly in May, rising 2.7 percent to 851 while they jumped 991 in Suffolk, a 13.5 percent rise.

Nationally, existing home sales rose 12.9 percent to a seasonally adjusted annual rate of 5.2 million compared to 4.6 million a year earlier.

“We’re making strides toward a healthy market in terms of the pace of activity,” said Celia Chen, a housing analyst for Moody’s Analytics. “House prices are rising and construction activity is picking up, home sales are picking up but the pace isn’t exceptionally strong.”