I don't know how serious this site is, but it says, its sources come from US Census.
There live less then 300.000 Arabs in America.
Number of Arabs in the United States
Because Arab Americans are not officially recognized as a federal minority group, it is hard to determine the exact number of Arab Americans in Michigan. The estimates range from 409,000 to 490,000 based on information from the Michigan Health Department and the Zogby International polls respectively. In the Greater Detroit area, estimates range from 300,000 to 350,000. While the latest Zogby polls rank Michigan's Arab-American population as second largest in the US, after California, Michigan's Arab-American community in Southeast Michigan still has the greatest local concentration .
Arab Detroit - Arab Americans
Really?