In this study, 0.1–4 wt.% Pd-loaded catalysts were synthesized via thermal decomposition of palladium (II) acetylacetonate (Pd(acac)2) at 210–310 °C or its photodecomposition under UV-LED irradiation using anatase TiO2 as a support. The catalysts were characterized by X-ray fluorescence, AAS, TEM, XPS, and CO chemisorption analyses and tested for CO oxidation at room temperature in a batch reactor both in the absence and presence of UV-LED irradiation. The effects of the Pd(acac)2 decomposition method and Pd content on the dark catalytic and photocatalytic activities were studied. Decomposition of Pd(acac)2 occurred with the formation of the metallic (Pd0) and oxidized (PdO) forms of palladium on the TiO2 surface for both employed methods. The photodecomposition resulted in an increased amount of metallic palladium. All of the synthesized Pd/TiO2 catalysts completely oxidized CO to CO2 at room temperature. UV-LED irradiation with a total irradiance of 10.4 mW/cm2 in the UVA region increased the rate of CO oxidation by up to 5 times compared to dark catalytic oxidation. Photodecomposition of Pd(acac)2 resulted in a higher activity of the Pd/TiO2 catalysts compared to the thermal decomposition method. The rate of CO oxidation under UV irradiation and under dark conditions monotonically increased as the Pd content increased due to the stability of high dispersion of Pd particles even with a high Pd content. The maximum value of the photonic efficiency was estimated to be 5.9%. CeO2, SiO2, and Al2O3 were also employed for the deposition of Pd to investigate the effect of a semiconducting support. For the CeO2-based catalyst, the activity under UV irradiation was higher than in the dark, but this effect was much lower compared to that of catalysts based on TiO2. By contrast, no substantial difference in the CO oxidation rate in the absence and presence of UV irradiation was observed for the non-semiconducting supports, SiO2 and Al2O3, confirming the photocatalytic oxidation of carbon monoxide for the TiO2- and CeO2-based catalysts.