Nassau County gained the most sales, growing by 24 percent to 764 for completed sales, and pending sales increased to 1,123, a 14.4 percent rise.
Suffolk County sales rose to 780 from 657 a year earlier, an 18.7 percent bump. Pending sales increased even more, climbing by 24 percent to 1,305.
The uptick in sales volume, said Maria Kafetzis, an associate broker at Douglas Elliman Real Estate in Plainview, is the product of five years of the market working through foreclosures after the crash and potential buyers adapting to more stringent lending standards.
"We're listing properties, and they're going in a couple of days," she said.
Higher sales volume continues a trend of rising transactions. Compared with the previous year, residential home sales volume has increased in all but two of the past 12 months in Nassau and all but one month in Suffolk.
The median price for a home sold in April dipped by 0.3 percent to $390,000 in Nassau compared with a year ago.
In Suffolk, the median rose by $15,000 to $300,000, a 5.3 percent increase compared with a year ago.
Multiple Listing Service president Kevin Leatherman said the overall county numbers mask the differences in the market that have emerged in the aftermath of superstorm Sandy.
"Along the whole South Shore there are some people doing a migration north," Leatherman said. "There's still people buying in those areas . . . [but] you have a shift in buyer behavior."
Houses farther away from the waterfront are appreciating in value while those in areas hit by flooding are not, he said.
"People who have lived through [the flooding] say, 'I'm not doing it again,' " he said.
Residential inventory -- the number of homes available for sale -- fell by 23.3 percent to 22,940 in the combined area of Nassau, Suffolk and Queens.