Abstract: For multimode vibration reduction of stay cables by supplementing damping, and to accommodate the design of bridge towers and girder where cables are anchored, this study is focused on dynamic modeling and multimode damping effect of in-plane vibrations of a stay cable with dampers attached on two or more locations. The modeling begins with the analytical modes of a cable without any dampers, and then introduces quasi-static correction modes for each damper installation position during modal truncation to reduce the number of cable modes required for numerical convergence, thereby improving computational efficiency. The system mass, stiffness, and damping matrices are derived for the general case when viscoelastic dampers, high-damping rubber dampers, and tuned mass dampers are installed on the cables simultaneously, considering the effects of cable sag and the inerter placed in parallel with the damper for damping enhancements. The established dynamic model meets the requirements for both damping effect evaluation and dynamic response analyses of the generalized cable damping system. Based on this model, a parametric analysis investigates the damping effects of systems with one external damper and two internal dampers, as well as systems combining internal and external dampers with tuned mass dampers. Furthermore, with reference to the particular design of the bridge tower of the Changtai Yangtze River Bridge, damping effects of two multi-point damping systems for the longest cable of the bridge are investigated. The results can provide guidance for the design of damping systems for the cables of this bridge and bridges alike.