This study examined the hypotheses that (1) sociodemographic risk factors in young children with autism spectrum disorders (ASD) and/or intellectual disability (ID) significantly vary by disability type, and (2) measures of income (mean adjusted gross income, mean federal taxes paid, and mean tax exemptions) significantly increase between 1994 and 2002, and are lower in families with a child with ASD and/or ID compared with the general population. A multiple source surveillance system utilizing a retrospective record review was used to identify ASD and ID cases from a population of 26,108 eight-year-old children born in 1994 and living in Utah in 2002. ASD without ID (ASD-only, n = 99) cases were significantly more likely to be male (P<0.01) and have mothers of White non-Hispanic ethnicity (P = 0.02). ASD with ID (ASD/ID, n = 33) cases were significantly more likely to be male (P<0.01) and have mothers older than 34 years (P = 0.03). ID without ASD (ID-only, n = 113) cases were significantly more likely to have fathers older than 34 years (P<0.01) and were significantly less likely to have mothers with >13 years education (P<0.01). Measures of income for cases at birth and at 8 years of age were not significantly lower than the general population and mean adjusted income of cases significantly increased from birth to 8 years of age. Investigations focused on defining early sociodemographic risk factors by different endophenotypes of ASD may assist in identifying risk factors for this complex group of neurodevelopmental disorders. Aggregate tax information may be a unique resource to utilize for population-based analysis. Autism Res2011,4:438–448. © 2011 International Society for Autism Research, Wiley Periodicals, Inc.