Movement in compliant mechanisms is achieved, at least in part, via deformable flexible members, rather than using articulating joints. These flexible members are traditionally modeled using Finite Element Analysis (FEA) based models. In this article, an alternative strategy for modeling compliant cantilever beams is developed with the objectives of reducing computational expense, and providing accuracy with respect to design optimization solutions. The method involves approximating the response of a flexible beam with an n-link/m-joint Pseudo-Rigid-Body Dynamic Model (PRBDM). Traditionally, static Pseudo-Rigid-Body Models (PRBMs) have shown an approximation of compliant elements using 2 or 3 revolute joints (2R/3R-PRBM). In this study, a more general nR-PRBDM model is developed. The first n resonant frequencies of the PRBDM are matched to exact or FEA solutions to approximate the response of the compliant system, and compared to existing PRBMs. PRBDMs can be used for co-design studies of flexible structural members, and are capable of modeling large deflections of compliant elements.