Los Angeles County’s seasonally adjusted unemployment rate dropped a half point in July to 5.1 percent, the lowest rate in four years as the local economy continued to perform strongly, the California Employment Development Department reported Friday.

The rate, which fell from 5.6 percent in June, mirrored a similar drop in the state unemployment rate, and reflected the still on-going boon in residential construction, as well as several large infrastructure projects. It was the lowest rate since April 2001 when it was a flat 5 percent.

Construction employed 147,600 people in July, up 0.4 percent from June and up 6 percent from July 2004. Those sectors benefited from intensifying construction activity at the ports, on the Metropolitan Transit Authority’s Gold Line light rail, and on hospital upgrades, said Jack Kyser, senior economist at the Los Angeles County Economic Development Corp.

Motion picture and sound recording employed 138,500 in July, down 2.2 percent from June but 14.2 percent higher than July 2004, thanks to increased location filming for reality TV.

Employment in the county, at just over 4 million non-farm jobs, was nearly flat, down 0.9 percent from June and up 1 percent from July 2004.

The greatest losses were seen in government and manufacturing. Manufacturing as a whole employed 476,700 people in July, down 0.5 percent from June and down 1.3 percent from July 2004, as jobs outsourced to overseas locations continued to take their toll.

Federal, state and local government employment was 560,800, down 4.8 percent from June and 1.5 percent lower than in July 2004.

Statewide, the seasonally adjusted unemployment rate dropped to 5.1 percent, the lowest rate since May 2001, and down from 5.4 percent in June and 6.2 percent in July 2004.