The U.S. Census Bureau news release is linked below.
U.S. Census Bureau: 1 Million Vietnamese Speakers
"A U.S. Census Bureau report released [September 11, 2013] says that there were 1.4 million people who spoke Vietnamese at home in the U.S. in 2011. Vietnamese was one of eight languages spoken by at least 1 million people."
---U.S. Census Bureau News Release