L.A. County’s unemployment rate fell to its lowest level in five years, driven by a thriving informal economy that appears to be growing with each passing month.

Countywide unemployment fell to 4.5 percent in September from a revised 5.0 percent in August and 6.3 percent in September 2004, according to the California Employment Development Department.

This came despite sluggish growth in overall payroll jobs. Only 12,000 jobs were added to L.A. County payrolls in September, and 34,000 jobs in the past year.

It’s in the unemployment data that L.A.’s hidden job market shows up. Unemployment figures, which are derived from a survey of worker households, take into account some temporary workers, independent contractors and other self-employed persons that don’t show up on company payrolls.

L.A. County’s unemployment rate hasn’t been this low since December 2000. At 4.5 percent, it is lower than the 4.8 percent national rate and the 5.1 percent seasonally adjusted rate for the state.

September was also the second straight month when L.A. County’s unemployment rate was lower than all surrounding counties except the 3.6 percent for Orange County, which has the lowest rate in the state.

Employment in L.A. County’s motion picture industry has risen by 11 percent over the past year, to 130,900. Business and professional services added 8,400 jobs to 572,100, while leisure and hospitality gained 8,100 jobs to 384,900.

Yet non-farm payrolls remained essentially flat in September, just above 4 million jobs. The manufacturing sector continues to lose jobs, and government jobs have also declined over the past year.