Los Angeles is the largest county in the United States by population, officially exceeding 10 million residents according to the United States Census on July 1, 2013. According to Bloomberg news, the population of L.A. is greater than that of 43 states! Yet, the executive and legislative branches of Los Angeles county government are controlled by 5 people (no wonder they are called the "The Five Kings").
In fact, Los Angeles is bigger than the sum of the second and third largest counties (Cook: Chicago metro and Harris:
Southern California has the 1st, 5th and 6th largest counties in the United States (Los Angeles, San Diego and Orange).
However, if you measure metro area population, the New York City area is still the largest, approaching 20 million, while Los Angeles metro exceeds 13 million (when you combine Los Angeles and Orange County).
Metro area Population
1. New York-Newark-Jersey City, N.Y.-N.J.-Pa. 19,949,502
2. Los Angeles-Long Beach-Anaheim, Calif. 13,131,431
3. Chicago-Naperville-Elgin, Ill.-Ind.-Wis. 9,537,289
4. Dallas-Fort Worth-Arlington, Texas 6,810,913
5. Houston-The Woodlands-Sugar Land, Texas 6,313,158
6. Philadelphia-Camden-Wilmington, Pa.-N.J.-Del.-Md. 6,034,678
7. Washington-Arlington-Alexandria, D.C.-Va.-Md.-W.Va. 5,949,859
8. Miami-Fort Lauderdale-West Palm Beach, Fla. 5,828,191
9. Atlanta-Sandy Springs-Roswell, Ga. 5,522,942
10. Boston-Cambridge-Newton, Mass.-N.H. 4,684,299
Interesting list. Curious that Phoenix (Maricopa County) is not in the Top 10, and that even though Houston is the largest city in Texas, Dallas metro is the largest metro area in the Longhorn Lone Star State.