Pasadena (pron.: /ËpÃ¦sÉËdiËnÉ/) is a city in Los Angeles County, California, United States. As of 2010 United States Census, the population of Pasadena was 137,122, making it the 180th-largest city in the United States, down from 168th place in 2009. Pasadena is the ninth-largest city in Los Angeles County, and on June 19, 1886, became the fourth to be incorporated in Los Angeles County, after Anaheim (February 10, 1870) and Santa Ana (June 1, 1886), which were part of Los Angeles County until Orange County was formed in 1889. It is one of the primary cultural centers of the San Gabriel Valley.