The median price of an existing Orange County home moved back above the $500,000 mark in September, while the pace of sales here remained sluggish, the California Association of Realtors said Friday.

The median price for an existing stand-alone OC home sold in September was $510,530, a nearly $11,000 or 2.2% increase from August, and a 2.8% increase from the prices homes here were selling at a year earlier.

The area’s median sales price now is up about 21% from the recent bottom of the market, seen in January 2009, according to the association’s figures.

Prices here are still off more than 31% from the peak of the market, when the median sales price for an OC home topped $747,000 in April 2007.

The number of OC home sales in September was up 1.6% from a month earlier, the Realtor association said.

Sales were down 10.4% from a year earlier.

The median sales price of an existing home in California was $309,900 in September, a 2.7% decrease from August and a 4.5% increase from a year ago, according to the association.

Sales in California were up about 3.8% from August’s levels, but were off nearly 12% from a year earlier. The inventory of homes priced under $500,000 remains “lean,” according to the association.

The association excludes condominiums from its figures.

Including condos, the median price of an OC home sold in September was $445,000, a jump of more than $16,000 or 3.7% from a year earlier, according to a report earlier this week from San Diego-based MDA DataQuick, a unit of Canada’s MacDonald, Dettwiler and Associates.