Source: World Sikh Council
http://www.wfn.org/2005/10/msg00132.html
On October 11, 2005 a World Sikh Council Press Release reported, "The World Sikh Council - America Region (WSC-AR) is pleased to announce that the 2010 Religious Congregations Membership Study (RCMS) [a statistical report published every 10 years by the Glenmary Research Center] will include a county-by-county population of Sikhs in the United States of America. Since the publication of the 2000 RCMS, which only included a listing of Sikh organizations at the county level, WSC-AR has worked with the Association of Statisticians of American Religious Bodies (ASARB) and the Glenmary Research Center (GRC) to expand the Sikh organization census reporting to include the Sikh population at the county level. Dr. Tarunjit Singh, Secretary General of WSC-AR, attended the 71st Annual Meeting of ASARB on Oct 4 - 5, 2005 at the headquarters of the Presbyterian Church (USA) in Louisville, Kentucky. During the meeting, WSC-AR affirmed Sikh representation in the 2010 survey... It is estimated that about 500,000 Sikhs live in the US but no breakdown of Sikh population at the county or state level is currently available."