A reliable autism spectrum disorder (ASD) diagnosis can occur as early as 18 months; however, the average age at diagnosis in the United States is over 2 years later. While there are numerous well-known barriers to seeking an ASD diagnosis, no research has examined if separation between a child’s biological parents affects timing of ASD diagnosis for their child. Data for this study were obtained from 561 children ( M age = 5.4 years, SD = 3.9 years) referred to an urban, outpatient ASD specialty clinic for their first ASD evaluation. Biological parents self-reported their relationship status during the evaluation, which was then categorized as either “together” (married or living together but not married) or “not together” (separated, divorced, or never married). An inverse-probability of exposure weighted linear regression model, which adjusted for 16 different child, family, and sociodemographic variables, was utilized to assess differences in child age of ASD diagnosis between groups. At the time of diagnosis, most children’s biological parents were together (69%) versus not together (31%). In the fully adjusted model, children of parents who were together were diagnosed 1.4 years earlier than those who were not together ( p < 0.001). Strategies for supporting these families and reducing age disparities are indicated. Lay abstract Autism spectrum disorder (ASD) can be diagnosed as early as 18 months of age. However, the average age at diagnosis in the United States is over 2 years later. A lot has been written about the many barriers families face when seeking a diagnosis for their child. One area of research that has received no attention is whether separation between a child’s biological parents affects the age at which a child is diagnosed with ASD. This study was conducted among 561 children who were receiving an ASD diagnosis for the first time. On average, these children were 5 years of age. The study took place in an urban, outpatient specialty autism clinic in the United States. Biological parents self-reported their relationship status during the evaluation. This was categorized as either “together” (married or living together but not married) or “not together” (separated, divorced, or never married). At the time of diagnosis, most children’s biological parents were together (69%). We found children of parents who were together were diagnosed 1.4 years earlier than those who were not together. These findings have important implications for providing support to families that separate early in a child’s life, with the goal of reducing the age at ASD evaluation among single parents and those who have been separated from their child’s other biological parent. Providing support to these families is important since earlier age at diagnosis leads to earlier intervention, which can improve long-term outcomes for the child, family, and community as a whole.