The month of May saw U.S. foreclosure activity fall 4 percent from May 2011, the 20th straight month to see a year-over-year drop, according to a report from foreclosure property marketplace RealtyTrac. Nevertheless, the number of housing units in some stage of foreclosure climbed above 200,000 for the first time in three months, the report said.

While certain hard-hit areas — in Arizona, California and Florida — are seeing a rebound in some aspects of their housing markets, such as increasing median list prices and dropping for-sale inventories, they are nonetheless struggling in other areas, including foreclosure filings.

For example, bruised California Central Valley metros Stockton and Modesto are still among the most battered by the foreclosure whirlwind — No. 5 and No. 6 on the May’s top 10 foreclosure rate list, respectively — despite more than 20 percent drops in their markets’ foreclosure rates from a year ago.

California metros, in fact, rank No. 2 through No. 6 on the top 10 list with Visalia-Porterville, Calif., which saw foreclosure filings occur at a rate of 1 in every 174 units in May, taking the California top spot.

The top spot overall, with a 231 percent foreclosure rate jump from a year ago, is Palm Bay-Melbourne-Titusville, Fla., with a foreclosure rate in May of 1 in every 170 units.

Atlanta-Sandy Springs-Marietta, Ga., and Phoenix-Mesa-Scottsdale, Ariz., where housing markets have rebounded in some respects in recent months, stood at No. 7 and No. 8, respectively, on the top 10 list.

Sustained, nationwide foreclosure activity doesn’t necessarily mean that the inventory of banked-owned properties will swell.

“Based on the rise in preforeclosure sales we’ve seen so far this year, a higher percentage of these new foreclosures starts will likely end up as short sales or auction sales to third parties rather than bank repossessions going forward,” said Brandon Moore, CEO of RealtyTrac, in a statement.

A deflection of foreclosures from eventual real estate owned (REO) status might be good for the market, Moore said. “Our first-quarter foreclosure sales report showed that the average price of a preforeclosure home was more than $27,000 higher than the average price of a bank-owned home.”

See the pages below for the top 10 U.S. metros with the highest foreclosure rates