A few facts of interest (mined from the County Judge's website, mostly) follow. Harris County is the nation’s third most populous county with nearly four million people, according to July 2008 estimates by the U.S. Census Bureau. Founded in 1836, Harris County has a larger population than 24 states. The area was originally named Harrisburg County after John Richardson Harris, an early settler of the region. The county’s name was changed to Harris County in 1839. Harris County is governed by Harris County Commissioners Court. The court is composed of a county judge and four commissioners. The county judge is elected countywide, and each commissioner is elected by Precinct. Twenty-nine Fortune 500 companies have headquarters in Harris County and more than half of the world’s 100 largest non-U.S. based corporations have operations in Harris County. Harris County is recognized as the Energy Capital of the world, with more than 5,000 energy related firms located here. The world’s largest medical center, the Texas Medical Center, is located in Harris County and employs 72,600. Harris County also is home to the Port of Houston, which is ranked first in the nation in volume of foreign tonnage and second in total tonnage. The Port of Houston is the seventh-largest U.S. container port and the second-largest petrochemical complex in the world. The City’s Houston Airport System is ranked as the fourth-largest multi-airport system in the nation and sixth worldwide. The system consists of an international airport, George Bush Intercontinental Airport, and two domestic airports, William P. Hobby Airport and Ellington Field. NASA’s Johnson Space Center is also located in Harris County and is home to the NASA astronaut corps and conducts training for United States space explorers and space station partner nations. The Johnson Space Center’s Mission Control Center directs all space shuttle missions, including international space station assembly flights.