Most of American Muslims identify as Sunni Muslims, with a smaller portion of the population identifying as Shi’ite Muslims.
It is hard to put an exact number of Sunni Muslims or Shi’ite Muslims in the United States because the US Census does not note the religion of permanent residents.
Schmidt, Garbi. “Islam in Urban America: Sunni Muslims in Chicago.” 1 Jan. 2004.
http://www.pewforum.org/2013/05/17/the-religious-affiliation-of-us-immigrants/#muslim