Two series of new lanthanide thiophosphates with partial Ca occupancy of the Ln sites, Cs_0.3(Ca_0.3Ln_0.7)PS₄ (Ln = Ce, Pr, Nd, Sm, Gd, Tb, and Dy) and Cs_0.5(Ca_0.5Ln_0.5)PS₄ (Ln = Pr, Nd, Sm, Gd, and Tb), were synthesized using a CsI flux and structurally characterized. The first series with an idealized formula of Cs_0.3(Ca_0.3Ln_0.7)PS₄ crystallizes in the Rm space group and belongs to a new structure type that consists of a channel containing [(Ca_0.3Ln_0.7)PS₄]^0.3− framework, where the channels are occupied by severely disordered Cs⁺ cations. A second new series with formula Cs_0.5(Ca_0.5Ln_0.5)PS₄ crystallizes in the monoclinic C2/c space group and exhibits a layered structure consisting of [(Ca_0.5Ln_0.5)PS₄]^0.5− layers with Cs⁺ cations located between the layers for charge balance. Together with the parent structure type, LnPS₄, these three structure types illustrate how the LnPS₄ structure changes with Cs⁺ cation incorporation, reducing its dimensionality from 3D to 2D. The magnetic properties of Cs_0.3[(Ca_0.3Ce_0.7)PS₄] and Cs_0.3[(Ca_0.3Pr_0.7)PS₄] were studied and revealed no magnetic transition down to 2 K.