The United States has the largest Chinese American community outside of Asia. According to the U.S. census, there are about 4.4 million Chinese American in 2013. Half of them lived either in California or New York State.
There are dozens of Chinatowns in United States. Just Greater New York already has at least nine of them.
Chinese American is more highly concentrated in metropolitan areas in the United States. The top three metro areas with the largest Chinese American populations are the Greater New York (about 735K in 2012), the San Jose-San Francisco-Oakland area (about 629K), and the Greater Los Angeles (about 567K).
In certain part of United States, Chinese American population is so high that Chinese becomes the second language in the areas. For instance, almost half of the population in Monterey Park of Los Angeles, CA is Chinese, 47.7% to be exact.
Continuing significant immigration from Mainland China, both legal and illegal, has spurred the ongoing rise of the Chinese American population. From 2000-2010, Chinese American population grew 40%. It increased in every state. 34 states experienced more than 50% increase. North Dakota and Nevada had even doubled the Chinese American population, 133% and 108% respectively.
In addition to the populations recorded by census, there are also a large number of Chinese visitors traveling in the United States. See Chinese Visitors in the U.S. [link to corresponding blog post]
(Source of all data above is U.S. Census www.census.gov)