Single motherhood has been associated with negative health consequences, such as increased risk for cardiovascular disease and depression, which might be accompanied by reduced levels of physical activity. This pilot study aimed to compare the magnitude of differences in physical activity between unmarried mothers, married mothers, and non-mothers. Participants (N = 66) in three equal-sized groups (n = 22) completed a battery of physical activity questions and wore an accelerometer for one week in March to May of 2012. Analyses of covariance controlling for group differences in demographic characteristics and Bonferroni post-hoc comparisons were conducted to detect differences in physical activity between groups. Compared to unmarried mothers, married mothers and non-mothers had significantly greater leisure time activity as measured by the Godin leisure-time exercise questionnaire (F(2,61) = 6.11, p = .004), overall activity in the previous year measured by the modifiable activity questionnaire scores (F(2, 61) = 8.65, p = .001), and minutes spent in moderate-to-vigorous physical activity from the accelerometer (F(2,58) = 4.39, p = .02). No statistically significant differences were observed among groups for international physical activity questionnaire scores or accelerometer activity and step counts. Overall, unmarried mothers were less physically active when compared to married mothers and non-mothers. Future studies should explore the correlates and health outcomes associated with physical activity among unmarried mothers.