Changes in tendon morphometry around first-row bones are linked to the hallux valgus (HV) development. However, there are very limited studies examining the relationship between the connection status of the tibialis posterior (TP) tendon to the adductor hallucis (ADH) and flexor hallucis brevis (FHB) tendons and the development of HV. This study aimed to investigate the association between these tendon connections and the occurrence of HV. The study included 24 formalin-fixed adult cadavers and amputee feet (10 female, 14 male). The attachment sites and connections between the ADH, FHB, and TP tendons were recorded. Feet were classified into three groups: no connection between the three tendons (Group I), connection between TP and FHB (Group II), and connection between TP, FHB, and ADH (Group III). HV angle values and subgroups (normal, mild, and moderate-severe) were defined to assess the degree of HV. Feet were grouped based on tendon attachment status, and the distribution of HV subgroups was statistically analyzed. HV angles in Group III were significantly larger than in Groups I and II (= 0.000, p = 0.024). While tendon connection was detected in only 20% (1/5) of feet without HV, tendon connection was detected in 64% (7/11) of mild HV and in all feet with moderate-severe HV. HV occurred in 93.8% (15/16) of feet with tendon connections (vs. 50% without). The study revealed that HV can develop in feet with and without tendon attachments. However, HV is more frequent in cases where the TP tendon is attached to the FHB and ADH tendons. Additionally, moderate-severe HV increases when TP is attached to ADH.