During the tremendous upswing in property values that helped define Loudoun County's growth after 2000, complaints about ballooning assessments poured in to county officials. Last year alone, the assessor's office received 7,500 calls.

But in the days since assessments were mailed this year, the phones at the County Government Center have been rather quiet, and some of the complaints have a new ring.

"Someone called and said they are trying to sell their house and it's assessed for $10,000 less than what they have it listed for, and they wanted the assessment increased," said county assessor Todd Kaufman.

Such are the signs of discomfort in long-booming Loudoun, as the impact of a real estate slowdown trickles down to the household level. Countywide, the average value of a single-family home dropped about 7 percent, reversing a trend in which home values in many parts of the county more than doubled from 2000 to 2006.

Not everyone has been hit the same way by the changes in the market. Residential assessments, for instance, were down about 5 percent in the Leesburg area but down about 9 percent in the Potomac District. Countywide, larger single-family residential properties -- those between an acre and 20 acres -- increased slightly in value. On the other hand, townhouses and condominiums in many areas took a significant hit.

"The diminished values in the condos and townhouses is what caused that much of a decline," Kaufman said. "There are about 35,000 condos and townhouses in Loudoun County, which is basically one-third of the housing market, which is a lot. If that percentage of the housing market takes a decline, it really impacts the assessments."

Townhouse values, for example, were down 9.5 percent in the Blue Ridge District and 9.3 percent in Dulles, according to county figures. People were so eager to become homeowners during the height of the market that many were willing to pay a premium, and builders were quick to try to capitalize on the demand.

"Things were coming on the market and selling very quickly, which of course caused somewhat of a feeding frenzy," Kaufman said. Then "everyone put their houses on the market at one time. . . . It's just simple supply and demand. They built too many of them too quickly, and the demand just dried out."

But Kaufman said he has seen indications of a rebound. "It's coming back already," he said.

Some of those who bought near the top of the market -- and recently received county tax notices showing their homes assessed for less than they paid -- said they are taking the long view of their investments.

Marie Dominguez bought her home in a neighborhood in the Broadlands subdivision where assessment increases in recent years had been among the highest in the county. In May, Dominguez's family paid $927,000 for their home on Glebe View Drive. Eight months later, Loudoun officials assessed it at $866,000, a nearly 7 percent drop.

""We bought at the tail end; we bought as things were coming down anyway. . . . We're not too worked up about that," Dominguez said. "We still have a child in high school. It's probably 15 years before we retire, so we're kind of here for a while. . . . I'm one of those believers that the market will go back up."