Toxic mortgages are no longer the leading cause of foreclosures in the United States. The country’s homeowners have a new leading enemy — unemployment.

Foreclosure filings during the first half of the year climbed in 75 percent of U.S. cities mostly because of the unemployment rate, according to a report released today by RealtyTrac Inc.

“Foreclosures are spreading out from areas that had been hardest hit,” Rick Sharga, senior vice president for marketing at RealtyTrac, told Bloomberg. “We’re dealing with underlying economic weakness as opposed to unsustainable home prices and bad loans.”

Cities in Nevada, Florida, California and Arizona accounted for the 20 highest foreclosure rates. But nine of the 10 largest metro areas had decreases in the total properties receiving filings. That could be a sign that foreclosures might have peaked in the states hurt most by the housing market collapse, according to RealtyTrac.

In June, foreclosure filings decreased 3 percent from the previous month and decreased 7 percent from June 2009. One in every 411 housing units in the United States received a foreclosure filing in June.

Iowa remained relatively sheltered in comparison to other states in June. One in every 1,787 homes in the state received a filing. But within the state, the metro areas suffered more than the rest of the state. One in every 801 homes in Polk County, one in every 491 homes in Linn County and one in every 909 homes in Scott County received foreclosure filings.

In Des Moines, one in every 676 homes received a filing. That compares favorably to cities such as Chicago (one of every 282), Ft. Lauderdale (one of every 138), Las Vegas (one of every 80), and Kansas City (one of every 249).