Background: Multiple types of individuals compose a mother’s social support network. Women may value opinions of individuals’ within their support network differently. Our study examined the relationship between breastfeeding opinions from individuals within the social support network and breastfeeding initiation and duration.Materials and Methods: Data from the Infant Feeding Practices Survey II were analyzed. The importance of individuals’ opinions on a mother’s breastfeeding decision was investigated for the baby’s father, the participant’s mother and mother-in-law, the infant’s pediatrician, and the participant’s obstetrician. The main outcomes were breastfeeding initiation (yes; no) and breastfeeding duration (weeks). Logistic regression provided the odds of never breastfeeding, while Cox proportional hazard models were used to assess the risk of breastfeeding cessation. Results: Women who stated that the father’s opinion was not at all important were more likely to never breastfeed and prematurely cease breastfeeding compared to women who stated that the father’s opinion was very important for their breastfeeding decisions. Conversely, women had lower odds of never breastfeeding and a decreased risk of breastfeeding cessation if they reported that the mother-in-law’s opinion was not at all important or not very important compared to women who reported that the mother-in-law was very important. No statistically significant relationship was found between the participant’s mother and breastfeeding initiation and cessation.Conclusion: This study found a hierarchical association between individuals in a social support network and breastfeeding initiation and duration. Inverse relationships were found between the importance of fathers’ and mother-in-laws’ opinions. Interventions aimed at increasing breastfeeding initiation, and duration rates should include a wider range of individuals within a social support network.