AbstractLow‐dimensional perovskites (LDPs) have attracted significant attention due to their high stability, great chemical flexibility, and fertile “playground” for structural modulation, which are expected to herald the next‐generation multifunctional devices. While there is a high diversity of LDPs in the literature, the organic cations in most of the literature are still limited to amines. Here, the preparation of centimeter‐sized LDP single crystals with amidino‐based spacers is described, which enables systematic investigations on how halides initiate different structural stacking and on their physical properties. The 4‐amidinopyridine (4AP) cation in (4AP)PbX₄ (X = Br, I) is vertically distributed between the inorganic layers to form a two‐dimensional perovskite. While the Cl‐based exhibits one‐dimensional perovskitoid packing. The change of halogens from Cl to Br and I leads to a lower hydrogen bonding, hardness and activation energy of the crystal. Finally, the potential of these crystals for X‐ray detectors is demonstrated. The (4AP)PbBr₄ device achieves the highest sensitivity among three devices (373.1 µC Gy_air⁻¹ cm⁻², 10 V), benefiting from the balanced charge transport and ionic migration. It is anticipated that this work will lead to further studies on the exploration and physics of novel LDP with properties suitable for radiation detection.