The TEAM force-field database is extended to cover room temperature ionic liquids (IL). The training set for parametrization includes 11 cations in five classes, imidazolium, pyridinium, pyrrolidinium, piperidinium, and tetraalkylammonium, and 12 anions, chloride, perchlorate, nitrate, tetrafluoroborate, hexafluorophosphate, thiocyanate, dicyanamide, tricyanomethanide, tetracyanoborate, bis(trifluoromethylsulfonyl)imide, triflate, and trifluoroacetate. The force field is compatible with other force fields of the TEAM database. The parameters are primarily derived from quantum-mechanical data, with a few nonbonded parameters optimized using experimental data of density and viscosity. The extrapolation of shear viscosity calculated using the nonequilibrium periodic perturbation (PP) method is examined by analyzing the Newtonian region in the calculated shear viscosities. With the identified extrapolation scheme, the PP method is about five times more efficient than the multiconfiguration-ensemble Green-Kubo (GK) method to reach similar convergence, and it is used for iterated calculations of viscosities as a part of the parametrization. The force field is validated using 46 ILs; the unsigned deviations from the experimental data are 1.4%, 12.8%, and 3.7% for density, viscosity, and isobaric heat capacity, respectively. The force field is used to analyze the interactions in terms of activation energies of viscosity and liquid structures in terms of distribution functions and free energy maps for common ILs. The ring-ring stacking is found to be the most stable local configuration for ILs of aromatic cation and chloride anion, which has a profound impact on the high viscosities of the ILs.