California

California was a state of the United States of America. Its major cities included Los Angeles and San Francisco. During the 20th century it was the location of the Mount Palomar Observatory; in the far future, the Los Angeles Crevasse would (presumably) be found here. The town of San Pedro here contained an overflow camp that was investigated by Torchwood. (TW: The Categories of Life)

New California was named for this state. (PDA: Synthespians™)

The Doctor regenerated here in 1999. (DW: Doctor Who)

Notable residents
Peri Brown was a resident of California at the time of her trip to Lanzarote, according to the unofficial, handwritten information at the beginning of her passport. (DW: Planet of Fire) Another account suggests her family was from Baltimore, Maryland. (PDA: Blue Box, BFA: The Reaping)

Dr. Grace Holloway was a homeowner and practising heart surgeon in San Francisco at the end of the 21st century. (DW: Doctor Who)

Before joining the CIA, Rex Matheson had lived in Los Angeles. After the CIA turned against him, he returned here with Torchwood to investigate PhiCorp. (TW: Rendition, Escape to LA)

Behind the scenes
Several stories have been set in California, including DW: Doctor Who, EDA: Vampire Science, Unnatural History; and TN: Wonderland — all set in San Fransisco —and the Los Angeles-based tales, PDA: The King of Terror; and TW: Escape to LA, The Categories of Life, and The Middle Men.