Sonoma County still leads the nation’s metropolitan areas for its rate of rent increases, with the average apartment this summer reaching $1,579 a month.

County apartment rents increased an average of 11.7 percent in the third quarter from a year earlier, according to Real Answers, a Novato-based rent research firm formerly called RealFacts.

The greater San Francisco metro area, including Alameda, Contra Costa, San Mateo and Marin counties, ranked second, with rents jumping 11.5 percent in the last year to an average of $2,285 a month.

Denver ranked third, its rents increasing 11.2 percent to $1,214. San Jose rents grew 10.5 percent to $2,369, the highest amount in the survey. And Vallejo-Fairfield ranked fifth with an increase of 8.7% and an average rent of $1,288.

While Sonoma County has seen rents soar 30 percent in three years, the city of San Francisco would rank “far and away higher” if considered alone rather than part of the greater metro area, said Real answers spokesman Nick Grotjahn.

Indeed, the county and other outlying communities in the Bay Area are seeing higher rents partly because of the number of workers seeking relief from the high cost of living in San Francisco and the Silicon Valley.

“Rents have skyrocketed in the employment centers,” Grotjahn said. A worker can find much cheaper housing by commuting from Petaluma to San Francisco.

The county’s rents also are rising due to local hiring and to a lack of new rental units. While two new apartment complexes will open in Rohnert Park and Santa Rosa in the coming months, they will be the first built here since 2008.

The county ended the third quarter with an occupancy rate of 97.5 percent, unchanged from a year ago. The rate essentially amounts to full occupancy, Grotjahn said.

The county’s third quarter rents varied from $946 a month for a studio to $2,179 for a three bedroom/two bathroom apartment. The average two bedroom/two bath unit went for $1,839.

While California’s rental market is leading the nation, Real Answers reports rising rents in every major metro area in the U.S. And the company doesn’t expect rate hikes to ease until occupancy rates start to decline.