Background: Although frailty is associated with disability, its long-term persistence and changes over time remain unclear. This study aimed to investigate the long-term association between frailty and the incidence of disability over a 10-year follow-up period, evaluating how this association changed over time. Methods: This cohort study was conducted in Okayama City, Japan. Community-dwelling older adults aged ≥65 years were included. Frailty was assessed using the Kihon Checklist, and disability was defined as a new certification for long-term care insurance. The association between frailty and disability was examined across five time periods (years 1–2, 3–4, 5–6, 7–8, and 9–10) using a marginal structural model with inverse probability of treatment weighting and inverse probability of censoring weighting. Results: The final analysis included 45,291 participants, with 17.3% classified as frail. The adjusted odds ratios (ORs) for the association between frailty and the incidence of disability gradually decreased over time but remained throughout the 10-year follow-up period. The adjusted ORs and 95% confidence intervals were 2.90 (2.55–3.29) for years 1–2, 2.40 (2.09–2.75) for years 3–4, 2.03 (1.76–2.34) for years 5–6, 1.75 (1.52–2.01) for years 7–8, and 1.58 (1.38–1.82) for years 9–10. Conclusion Frailty was consistently associated with the incidence of disability over a 10-year follow-up period, with a stronger association in the earlier years and a gradual decline over time.