The median home price in Los Angeles County surged in July to $543,890, a 20.4 percent gain from the like period a year earlier, according to a report released today by the California Association of Realtors.

The percentage gain in L.A. County outpaced the statewide 17.1 percent increase, to $540,900.

Five of the state’s top 10 cities with the highest median home prices are in Los Angeles County: Palos Verdes Estates ($1.6 million); Beverly Hills ($1.5 million); Manhattan Beach ($1.4 million); Calabasas ($1.3 million); and La Canada-Flintridge ($1.2 million).

Jim Hamilton, the association’s president, attributed the continued strength of the housing market to low mortgage rates, along with an improving national and state economy that has led to higher household income levels.

The gains in L.A. County were stronger than other areas of Southern California, which cooled to single-digit appreciation levels. The median home price in Orange County increased 9 percent from a year earlier, to $706,820, and the median price of a San Diego home rose 5.8 percent from a year ago, to $616,050.

Home stayed red hot in Riverside and San Bernardino, where the July median price rose 21.1 percent from a year ago to $384,910.

CAR gets its home price information from a survey conducted by the Multiple Listing Service of more than 90 associations of Realtors throughout the state. The data tracks closed escrow sales of existing single-family homes in California. Numbers reported by the Business Journal earlier this month and based on data from Home Data Corp. showed a median price of $515,000 in July, up 20.6 percent from a year earlier.

On a year-over-year comparison, the number of homes sold during July in Los Angeles and Orange County rose by 2.9 percent and 36.5 percent, respectively, according to the CAR.

Except for Monterey County, the number of homes sold in July fell from June’s volume in every area of the state. Leslie Appleton-Young, the association’s chief economist, said that’s not unusual.

“Historically, June accounts for the largest share of annual sales, and there typically is a month-to-month decline in sales from June to July in the regional and county sales figures,” she said in a statement.

By the end of the year, Appleton-Young expects a 1.4 percent increase over the record-setting number of homes sold in 2004.