The number is small, according to Pew, but it is growing:
Pew Research Center estimates that there were about 3.3 million Muslims of all ages living in the United States in 2015. This means that Muslims made up about 1% of the total U.S. population (about 322 million people in 2015), and we estimate that that share will double by 2050.
Our new estimate of Muslims and other faiths is based on a demographic projectionthat models growth in the American Muslim population since our 2011 estimate and includes both adults and children. The projection uses data on age, fertility, mortality, migration and religious switching drawn from multiple sources, including the 2011 survey of Muslim Americans.
According to our current estimate, there are fewer Muslims of all ages in the U.S. than there are Jews by religion (5.7 million) but more than there are Hindus (2.1 million) and many more than there are Sikhs.
In some cities Muslims comprise significantly more than 1% of the community. And even at the state level Muslims are not evenly distributed: Certain states, such as New Jersey, have two or three times as many Muslim adults per capita as the national average.