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The fires that ravaged the North Bay in October have resulted in about $9 billion in insurance claims, triple the figure of a month ago, according to new data released Wednesday by the state Department of Insurance.

The lion’s share of claims from the fires — almost $7.5 billion — are from Sonoma County, including $6.9 billion in losses for residential property. There were 4,785 county policyholder claims filed for total loss of property, while another 9,901 filed for partial losses or smoke damage.

The North Bay blazes that started Oct. 8 have become the costliest wildfires in American history in terms of insured loss. The 1991 Oakland Hills fire had previously held that title, with $1.7 billion in insured losses at the time, according to the Insurance Information Institute, a national industry trade organization that compiles claims data. The costliest disaster in American history remains Hurricane Katrina in 2005, with $41.1 billion in insured losses.

“These numbers not only represent staggering losses to tens of thousands of Californians,” state Insurance Commissioner Dave Jones said in a statement. “The October wildfires that devastated whole communities and tragically cost 44 people their lives have now proven to be the most destructive and deadliest in our state’s history.”

Napa County had more than $1.2 billion in overall insured losses, with 447 houses destroyed and another 2,023 properties with claims for partial destruction. Mendocino County had $181 million in losses, while Lake County suffered $52 million in insured claims.

The fires also resulted in a significant loss of vehicles, with almost 4,900 claims filed for destroyed personal and commercial cars and trucks in the region. In Sonoma County alone, 4,173 policyholders filed insurance claims on their vehicles, resulting in almost $70 million in damages.

More than $3 billion in claims have been paid to date by insurers, according to Jones, including almost $2.5 billion in Sonoma County.

About a third of insured claims have been paid for homeowner losses in the county so far, according to the data.

Homeowners, however, may find themselves underinsured in the rebuilding, depending on their policy, especially if they had not readjusted their coverage in many years or opted for more frugal coverage.

Contractors said the cost of rebuilding will rise over the next year because of an increase in the prices of building materials as well as the scarce availability of labor.

Those who have an extended replacement cost policy will be in much better shape because those policies pay a specified percentage over the policy limit to fully replace a damaged home — some up to 150 percent of the limit — or include specific coverage that provides for building code upgrades.

The department is hosting a workshop Saturday at The Glaser Center at the Unitarian Universalist Congregation of Santa Rosa, where residents can ask insurance questions of its personnel. The event runs from 10 a.m. to 4 p.m. Those who want a one-on-one counseling session are asked to call 800-927-4357 beforehand to reserve a spot.

You can reach Staff Writer Bill Swindell at 707-521-5223 or bill.swindell@pressdemocrat.com. On Twitter @BillSwindell.