Fluid viscous dampers have been widely applied to reduce the effects of vibrations in civil engineering structures. A good understanding of the dynamical behavior of these devices is required to analyze structures equipped with fluid viscous dampers. The simple Kelvin–Voigt and Maxwell rheological models do not have enough parameters to suitably capture the frequency dependence of device parameters, so other models representing some generalizations of the basic Kelvin–Voigt and Maxwell models have been developed. This paper deals with parameter identification for basic and generalized Kelvin–Voigt and Maxwell models for fluid viscous dampers. The identification procedure gives the best mechanical parameters by minimizing a suitable objective function that represents a measure of difference between analytical and experimental applied forces. For this purpose, the particle swarm optimization is adopted. Results are obtained under various test conditions, comparing the agreement of various models with experimental data. Finally, a numerical investigation is performed on a simple one degree of freedom structure, equipped with fluid viscous dampers and subject to a real seismic motion.