It’s a problem that Washington, D.C. resident Peter Wilson knows all too well. He was able to sell his home last year—within a week—after putting it on the market after Labor Day. But since then, he’s been a renter because he can’t find a home he wants to buy in the Mount Pleasant neighborhood of Washington.

And given the tight market, some sellers aren’t even making much of an effort to get their home ready for sale, he said.

“I went to one open house—it was like they decided the night before to put their house on the market,” he said. There were dishes in the sink and a messy walk-in closet with clothes and toys completely covering the floor, for example. And several bills were left out on the dining room table.

The home was off the market in a week, Wilson said.

Falling inventories

On a national basis, listed inventory was down 20.4% in May, compared with May 2011, according to recent statistics from the National Association of Realtors. There’s a 6.6-month supply of homes, given the current pace of sales. Read more: Sales of U.S. existing homes fall 1.5% in May.

In some local areas, however, the plunge has been much steeper.

The inventory of homes for sale in King County, where Seattle resides, was down 43.8% in May, compared with a year ago, according to Redfin, a national brokerage based in Seattle. In the District of Columbia, inventory was down 34.2% over the year. Inventories were down 37.9% in Sacramento County, Calif., 34.3% in Maricopa County, Ariz., where Phoenix is located, and a whopping 54.9% in Orange County, Calif.

Of course, it’s important to point out that this inventory shortage isn’t being seen everywhere. In Cook County, Ill., where Chicago is located, inventories are only down 3.9% over the year. And in Suffolk County, Mass., where Boston is located, inventories are actually up 4%.

It’s also important to remember that within markets there are areas that are more popular than others, and more likely to have tighter inventories.

What’s going on?