Research interest in reliability and sensitivity analyses of concrete dams has grown in recent decades, yet existing studies remain largely limited to gravity and arch dams and to case studies focused on earthquake events. To address this gap, this study aims to evaluate the reliability and sensitivity of concrete buttress dam monoliths using a simulated population based on existing Swedish designs with varying geometric properties such as height and width. Three failure modes, sliding, overturning, and combined sliding and overturning, were assessed under ice load and overtopping conditions. Reliability indices and local sensitivity measures were first estimated using first-order reliability analysis, after which polynomial chaos expansion metamodels were constructed to facilitate global sensitivity analyses. The results show that sliding has the lowest reliability, whereas overturning exhibits very high reliability and is generally not governing. Local sensitivity analyses indicate that rock-concrete interface friction dominates sliding and the combined failure mode, while concrete density is most influential for overturning. Global sensitivity analyses show that sliding reliability is primarily affected by front plate inclination, while overturning is mainly relevant for low monoliths or those with near-vertical front plates, and the combined mode is mainly influenced by asperity and front plate inclinations.