Whatcom County’s unemployment rate dropped from 5.4 percent in September to an estimated 5.2 percent in October, according to the latest date from the state Employment Security Department.

That’s the county’s lowest unemployment rate since 2008, but it doesn’t reflect the nearly 600 layoffs that CH2M Hill and Alcoa Intalco Works announced in the last few months.

The layoffs at CH2M Hill’s Bellingham office begin sometime after Dec. 7, according to a notice filed with the state Employment Security Department. They plan to lay off 128 workers.

Alcoa will layoff 465 employees from its Intalco Works smelter west of Ferndale beginning early next year, according to an Employment Security Department notice.

The latest report estimates that the county gained 3,800 jobs in the past year. Of those jobs, 3,100 are in the private sector and 700 are in the public sector. Most of the new jobs in October and in the last year are in construction, according to the report.

The county’s civilian labor force — the number of people 16 and older who are not in the military and either have a job or are seeking a job— grew by 145 people to 102,655 in the last year.

The state’s seasonally adjusted unemployment rate dropped from 4.8 in September to 5.0 in October. The county numbers from the Employment Security Department are not seasonally adjusted and therefore should not be compared directly to the statewide rate, the department warns.

Skagit County’s unemployment rate for October was 5.9 percent. King County had the lowest unemployment rate in the state, at 4.1 percent for the month. Ferry County, in northeast Washington, had an unemployment rate of 8.6 percent, the state’s highest.