Poor mental health is a highly prevalent and serious public health issue, and it is particularly prevalent in vulnerable, high-risk populations such as single mothers. Single mothers have consistently been found to have higher odds of poor mental health than non-single mothers. Poor mental health is commonly analyzed as a biological problem, and much of the current literature does not address environmental variables that may potentially mediate the relationship between single motherhood and poor mental health. The purpose of this investigation was to use the 2009 Behavioral Risk Factor Surveillance System (BRFSS) survey to determine the relationship between relationship status and mental health status in mothers in a national representative sample, noting the disparity between single and non-single mothers and addressing potentially mediating variables which might better explain the observed health disparity. Statistical analyses were conducted using 65,233 mothers with complete data. Due to the large sample size, a significance level of alpha = 0.00001 was used. Poor mental health was assessed using the Frequent Mental Distress question from the core component of the BRFSS survey. Keeping with convention, those mothers reporting 14 or more days of frequent mental distress in the past 30 days were considered to have poor mental health. The bivariate results demonstrated that, without accounting for other variables, single mothers had higher odds of self-reporting poor mental health than non-single mothers (Never-Married OR = 1.530, 99.999% CI 1.130, 2.070; Divorced OR = 2.286, 99.999% CI 1.753, 2.982; Widowed OR = 1.830, 99.999% CI 1.159, 2.890; Separated OR = 2.797, 99.999% CI 1.863, 4.200). This finding was consistent with the current literature. However, after building a multiple logistic regression model and adjusting for socioeconomic status and social and emotional support, relationship status was no longer significantly associated with mental health status. This indicates that relationship status is a surrogate measure of socioeconomic status and social and emotional support, and that these variables might better explain the observed disparity. The results of this investigation imply that future interventions tailored for single mothers should address socioeconomic status and social and emotional support networks. More research is needed to determine potential causal relationships between socioeconomic status, social and emotional support, and mental health status.