Descriptive Epidemiology of Autism in a California Population: Who Is at Risk? ("Increased risks were observed for males, multiple births, and children born to black mothers."). The second I found was the review article The Epidemiology of Autism Spectrum Annual Review of Public Health Vol. 28: 235-258. The find little evidence of racial differences in frequency and cite Schieve LA, Rice C, Boyle C. 2006. Mental health in the United States: parental report of diagnosed autism in children age 4–17 years–united states 2003–2004. MMWR 55:481–86 who found no difference in reported diagnosis rates between black and white Americans. Wikipedia cites another survey, New Developments in Autism Psychiatric Clinics of North America, Volume 32, Issue 1, Pages 1-14, which says
No well-established studies have consistently identified differences in the rates of autism across ethnicities or demographic backgrounds.
Therefore, most professionals maintain a belief that the occurrence of autism is not influenced by economic, social, racial, or ethnic background.