Research examining parental reports of children's living arrangements has often relied on information about legally ordered custody agreements following divorce. This analysis used data from matched pairs of parents (N = 1,156) in the Fragile Families and Child Wellbeing Study who live apart to compare mother and father reports of their child's residence 5 years after a nonmarital birth. The authors found that over one third of unmarried parents disagreed about who their child lived with and that conflicting reports were much more likely when fathers spent nights with the mother (an indicator of part-time cohabitation) and had overnights with the child on their own. The results further suggest that discrepancies in unmarried parents' reports were more closely associated with the complexity and ambiguity of their living situations than with the quality of their relationships with each other. Implications for measuring children's living arrangements in families formed outside of marriage are discussed.