Objectives: The aim of this research was to investigate general population attitudes and knowledge regarding Hashimoto disease, particularly the association between diet or dietary supplements with thyroid health. Materials and Methods: The study was approved by the Ethics Committee of the University of Split, School of Medicine, and conducted in June 2024. Data collection utilized an online survey distributed via social media to 448 participants from Croatia. Participants provided informed consent before completing the questionnaire. Results: The study included predominantly female participants (93.7%), primarily aged between 21 to 30 years (60.3%), and holding master’s degrees (51.6%). Out of 448 participants, 74 (16.6%) reported having thyroid disease. Among those with thyroid conditions, 79.7% believed that diet impacts the course of thyroid disease. However, only 20.3% followed specific dietary regimens for thyroid health, despite 60.8% using thyroid medication and 36.5% using dietary supplements. Participants who had their thyroid hormones checked were more likely to believe in the positive impact of diet and supplements on thyroid health. Overall, 91.2% of participants had an opinion on diet affecting thyroid function, with a significant proportion associating increased vegetable intake with positive thyroid health, while gluten was least associated. Additionally, iodine was reported by the majority (62.3%) as having a positive effect on thyroid health, whereas Inositol and Ashwagandha were the least associated with positive effects. Conclusion: This study highlights varied beliefs and practices regarding thyroid health management among the Croatian population. It underscores the need for targeted educational initiatives to bridge gaps between belief and practice in diet and thyroid health. Enhancing awareness and support through clear dietary guidelines and healthcare provider education could improve outcomes for individuals managing thyroid conditions. Future research should consider diverse demographic representation and qualitative methods to explore barriers and facilitators of dietary management in thyroid health.