Passenger traffic in and out of Charles M. Schulz-Sonoma County Airport (STS) in December totaled 32,263, up 3.3 percent from December 2017, according to figures released Thursday.

December’s individual airline counts show that Alaska reported 29.7 percent growth, serving 26,490 passengers. Load factor — a metric for how full the seats are — was 81 percent for the month, up 11 percent from December 2017.

American Airlines posted a 37.3 percent decline in passengers, serving 3,596 passengers in December. Its load factor was 79 percent, up 14.5 percent from last December.

United’s tally saw a 59.5 percent decline in December passenger traffic compared to the same month in 2017. The airline served 2,031 passengers last month, with a monthly load factor of 68 percent, up 17.2 percent from December 2017.

Seasonal flier Sun Country reported a large increase in passengers for December, up 156.1 percent over December 2017. It served 146 passengers in December at a load factor of 58 percent, up from 65.7 percent from last December.

But the bigger story is the airport reached an all-time high in passenger traffic for 2018, with a total of 440,644 passengers served. That’s a 10.8 percent increase over 2017’s final count of 397,787 passengers.

“We achieved this new annual record due to increased passenger service by Alaska, American and United,” said Jon Stout, airport manager. The bulk of the increase came from Alaska, which increased flights 6 percent over 2017, he said.

American Airlines, which trimmed service from two flights to one per day, still performed well, according to Stout.

“Even though they decreased flights by 20 percent in 2018, passenger volume only decreased by 7 percent,” Stout said, explaining the planes on the existing flight were fuller. “Those flights are very healthy, and (American) has indicated they’re strong in our market with the announcement of the Dallas flight coming in June.”

All indications look healthy for the airport this year.

American announced last month its upcoming service between Santa Rosa and Dallas-Fort Worth, along with service to Los Angeles starting up in May.

On March 8, United will start a once-daily route to Denver — a key, direct link to a significant hub. The airline, which made the announcement in August, currently offers a 17-minute trip from Santa Rosa to San Francisco International Airport, encouraging travelers to make connections to other flights.

Sun Country is poised to build on its success in the market for a third consecutive year by resuming — and expanding — nonstop seasonal flight service between Santa Rosa and Minneapolis-St. Paul. Seasonal service to Las Vegas also will return. Information will soon be available about start dates.

“It was a banner year for the airport in the county,” Stout said. “We expect this year to top last year.”