Existing literature has documented the associations between marital status and maternal depression within the first year postpartum. Using data that is representative of urban non-marital births in the United States with a large over-sample of non-marital births, we investigate the association of maternal depression with not only marital status but also relationship quality with the father of the baby. Quality is independently associated with maternal depression after controlling for marital status and other variables that have been documented as risk factors for maternal depression. In addition, relationship quality explains away the associations between marital status and maternal depression. After controlling for relationship quality, single women were no more likely to be depressed compared to married or cohabiting women.