Increase (July 2005 - July 2006): 81,411
Riverside County runs from Orange County all the way to the Arizona border. It encompasses huge amounts of Mojave Desert, with occasional oases, mountains and cities for variety.
The county's rapid growth can be traced to its proximity to Los Angeles; many of the new residents are Angelenos searching for less expensive homes.
There are also numerous recreational and retirement communities here, including the longtime playground for Hollywood stars, Palm Springs.