Located in Southern California, Los Angeles County was created when California became a state, and as of date is also its most populated. Originally it consisted of its current area and Orange, San Bernardino, and Kern counties. The county was broken-up into these individual ones between 1853-1889. The county has one of the most powerful municipal bodies in the United States, the five-member Los Angeles County Board of Supervisors.
The county seat, is obviously, Los Angeles and the northern 1/2 of the county is effectively barren desert with only Palmdale and Lancaster as its major cities.
Sources
Pitt, Leonard/Dale. Los Angeles: A to Z: An Encyclopedia of the City and County