To determine the influence of the lanthanide size on the structures and properties of thiophosphates, a thiophosphate series containing different lanthanides was synthesized via high temperature flux crystal growth and their structures and physical properties analyzed and compared. Layered thiohypophosphates NaLnP2S6 (Ln = La, Ce, Pr) and thiopyrophosphates CsLnP2S7 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Y) were grown out of an iodide flux using consistent reaction conditions across both series. Under the mildly reducing iodide flux reaction conditions, a rather rare example of phosphorus reduction from the +5 to the +4 oxidation state was observed. Both resultant structure types are based on lanthanide thiophosphate sheets with the alkali cations located between them. Magnetic susceptibility measurements were conducted and revealed Curie-Weiss behavior of the samples, with a Van Vleck contribution in the CsSmP2S7 sample. UV-vis data was found to be in good agreement with the literature, indicating little influence of the sulfide environment on the localized 4f orbitals.