<p>A novel thiazole-pyridine Schiff base chemosensor, N-(4-(4-chlorophenyl)thiazol-2-yl)-1-(pyridin-4-yl)ethan-1-imine (CTPE), was synthesized via acid-catalyzed condensation of 2-amino-4-(4-chlorophenyl)thiazole and 4-acetylpyridine, and characterized by ¹H NMR, ¹³C NMR, FT-IR, and HR-MS spectroscopy (HR-MS: m/z = 314.2456 [M + H]⁺; A significant pale yellow-to-brown change in color and a UV-Vis hypsochromic shift from 281 to 274&#xa0;nm are produced by CTPE’s extremely specific colorimetric reaction to Fe³⁺. Bidentate N, N′-chelation through the imine and pyridine nitrogen atoms is confirmed by the elimination of the C = N band at 1528&#xa0;cm⁻¹ and the appearance of a new Fe-N band at 428&#xa0;cm⁻¹ upon Fe³⁺ coordination. The sensor shows a 1:1 binding stoichiometry and an ultralow detection limit of 0.02371 µM, a value significantly lower than the 5.37 µM U.S. EPA permitted limit for iron in drinking water. With EDTA regeneration, the sensor is reversible and reusable in pH ranges of 4 to 10. Recoveries of 94–105% with low RSDs were obtained from spiked tap and pond water samples, demonstrating practical use. With a HOMO-LUMO gap of 3.53&#xa0;eV for free CTPE narrowing during Fe³⁺ complexation, consistent with enhanced charge transfer upon binding, DFT calculations (B3LYP/6-311 + + G(d, p)) validate the experimental results. These findings establish CTPE as a reasonably priced, lightweight, reusable, and selective colorimetric platform for rapid Fe³⁺ detection in analytical and applications in the environment.</p>