Background: Some breastfeeding mothers try to increase their milk supply through pharmaceutical, dietary, and behavioral strategies that vary in effectiveness. Information seeking behaviors may influence which strategies mothers use. Objective: To describe where mothers obtain information about increasing milk supply, describe the perceived influence of each information source on decision-making about strategies for increasing milk supply, and explore associations between information sources and mothers' use of galactagogues (i.e., pharmaceutical and dietary strategies) and behavioral strategies. Methods: Women who were currently breastfeeding and living in the United States were recruited through Facebook advertisements to complete an online survey between December 2020 and February 2021. Descriptive statistics were calculated, and chi-square tests compared participants' use of galactagogues and behavioral strategies by information sources. Results: Participants were 1,351 breastfeeding mothers (81% non-Hispanic white; 47% first-time breastfeeding; 21% Special Supplemental Nutrition Program for Women, Infants, and Children participants). Nearly all participants (97%) obtained information about increasing milk supply from at least one source, most commonly lactation consultants (68%), Facebook (61%), search engines (50%), websites (47%), and nurses (41%). There was high variability in the perceived influence of each source on decision-making. Galactagogue use was higher among participants who obtained information from the internet (Yes: 68% vs. No: 43%, p < 0.000), social media (Yes: 65% vs. No: 40%, p < 0.000), family and friends (Yes: 65% vs. No: 53%, p < 0.000), and lactation consultants (Yes: 63% vs. No: 54%, p < 0.002). Behavioral strategies were more commonly reported among participants who accessed these same sources, maternal health care professionals (Yes: 98% vs. No: 91%, p < 0.000), and pediatricians (Yes: 98% vs. No: 94%, p = 0.001). Conclusion: Breastfeeding mothers commonly obtained information about increasing milk supply from a variety of sources. Information sources accessed were associated with mothers' use of galactagogues and behavioral strategies for increasing milk supply.