This study examined associations between self-reported cognitive functioning and social support as well as social ties among women with breast cancer. The study included 3351 women from the Women’s Health Initiative Life and Longevity After Cancer cohort who were diagnosed with breast cancer stages I-III. Social support was assessed using a modified Medical Outcomes Study (MOS) Social Support Survey, and marital status was obtained from the baseline questionnaire. We also assessed social ties (e.g., number of friends, relatives, living children) and cognitive function (Functional Assessment of Cancer Therapy-Cognitive Function [FACT-COG]) on the year-1-follow up questionnaire. Multivariable quantile regression was used to estimate the changes in median cognitive scores. Kruskal-Wallis tests were used to assess the association of cognitive function with social ties. The majority of participants were non-Hispanic White (93.3%), presently married (49%), with at least a 4-year college degree (53.2%), and had been diagnosed with localized breast cancer (79%). A 10-point higher social support score correlated to a 0.32 higher (better) median cognitive score (p < 0.001). Women who were presently married tended to have better cognition than women who were divorced/separated or widowed (p = 0.01). Significant associations were also present for having close relatives (p < 0.001) or friends (p < 0.001), with cognitive scores being higher in those with at least one close relative or friend compared to none. Women reporting higher social support and greater numbers of friends or relatives have higher cognitive functioning. Compared to divorced or separated women, married women were likely to have higher cognitive functioning. These findings suggest that social support assessments have the potential to help identify women at higher risk of cognitive decline.