How Many Sikhs Are There in the US?

Yesterday's news produced a horrible example of a hate crime--another situation of xenophobia and its byproducts. A gunman entered a Sikh temple in Milwaukee, Wisconsin and killed six people and wounded three others. The New York Times reports that the shooter (who was killed by police during a gun battle) "had long been among the hundreds of names on the radar of organizations monitored by the Southern Poverty Law Center because of his ties to the white supremacist movement and his role as the leader of a white-power band called End Apathy. The authorities have said they are treating the shooting as an act of domestic terrorism."

Sikhs are members of a religious group that originated in the Punjab region of India, and males are characterized by wearing turbans. This has the unfortunate side-effect of setting them apart and, in particular, creating a situation in the US where they have been mistaken for Muslims and discriminated against on that count, if not on others.

Of some interest demographically is that the first reports of the tragedy indicated that there are 500,000 Sikhs in the United States. My first thought on hearing this was that it is almost certainly way too high. An Associated Press story in the Washington Post notes that:

The exact number of Sikhs living in America is not known. Estimates range from 200,000 to 500,000. Many left their homes in the agricultural Punjab province, known as the breadbasket of India, and arrived first in the West and Pacific Northwest in the late 1800s.
The first major temple was built in 1912 around Stockton, Calif., but like other immigrants, Sikhs were not allowed to bring their spouses to the United States, which restricted their numbers. When President Lyndon Johnson eased immigration quotas in the 1960s, Sikhs began arriving in larger numbers with their families. Temples were built around Boston, Chicago and other parts of California.

It is a reasonable assumption that a large fraction of Sikhs in the US were born in India. The Migration Policy Institute shows that the 2010 ACS data from the census indicate that there are about 1.6 million people living in the US who were born in India. How likely is it that one-third of them are Sikhs? We can't know for sure, of course, since questions on religion are not asked on the US census. However, starting in 2001, the UK census has asked about religion. The 2001 data suggest that there were 552,000 Hindus in the UK and 329,000 Sikhs. If we assume that Hindus and Sikhs represent the vast majority of immigrants from India, then Sikhs account for 37 percent of those of Indian origin in the UK. If we then assume that the regional pattern of migration from India to the UK is the same as from India to the US, we could easily arrive at the idea that at least a third of the people of Indian origin in the US are Sikhs--a number very close to 500,000.