Importance: Impedance monitoring is a critical component of cochlear implant (CI) surgery, yet the lack of comprehensive longitudinal data limits the development of evidence-based postoperative monitoring guidelines, potentially compromising patient outcomes. Objective: To track impedance trends over 10-years post-implantation, evaluate the effects of electrode design on impedance dynamics, and examine the influence of patient age on impedance behavior. Design: Retrospective cohort study. Setting: Tertiary medical center. Participants: A total of 554 ears underwent cochlear implantation between June 2006 and December 2014; each ear received 1 electrode array from 1 of 6 electrode types. Exposure or Intervention: Longitudinal impedance data were analyzed across apical, medial, and basal electrode contacts at 7 time points. Main Outcome Measures: Impedance trajectories varied by age group, electrode design, and cochlear region, with persistent changes observed up to 10-years. Results: Impedance increased markedly from intraoperative to first activation in most arrays, although a significant decrease in apical contacts was observed in CI512 adults (P-=-.0008). Apical and medial contacts generally stabilized or declined thereafter. In contrast, basal electrodes exhibited more heterogeneous patterns, including increases during 12 to 60-months of follow-up and decreases during 60 to 120-months. Compared to PM arrays, LW electrodes showed higher apical impedances, medial impedances that were mostly comparable and time-dependent, and persistently lower basal impedances than CI512. Among LW arrays, CI422 consistently demonstrated the highest impedance, whereas the MED-EL electrode series, Flexsoft exhibited the highest impedance. Overall impedances were higher in early childhood recipients, while adults tended to show higher values in the basal region. Conclusion: This study provides the first decade-long characterization of impedance changes, revealing dynamic variations in electrode impedance across different designs and age groups of cochlear implant recipients. Relevance: This study highlights the need for long-term monitoring and offering practical guidance for individualized programming and electrode design.