Mercury (Hg), though naturally occurring, is a toxic element. Exposure to various forms of mercury can be harmful for humans and ecosystems. Mercury-contaminated wastewater can be treated using activated carbon to adsorb the mercury, allowing for safe discharge. Wet chemical oxidation of activated carbon was performed to enhanced surface oxygen functionality, with the objective of enhancing aqueous ionic (Hg(II)) and elemental (Hg(0)) mercury adsorption. Characterization of the modified carbons included nitrogen adsorption-desorption, elemental analysis, point of zero charge, and total acidity titration. The concentration and identity of the modifying reagent influenced the characteristics of the carbons, including the surface oxygen functionality. These carbons with enhanced surface oxygen (C(O)) were applied to trace-level Hg solutions (50 μg/L). Adsorption of Hg(II) demonstrated a strong positive correlation with the carbon’s oxygen content, with the greatest Hg(II) removal associated with the highest oxygen content. Interestingly, this correlation was not seen in Hg(0) adsorption. A four variable model best fit the data, identifying surface area, pore volume, point of zero charge, and oxygen content as important variables. The point of zero charge was identified as the primary independent variable. To ensure proper waste handling, it was determined that none of the carbon samples leached mercury at levels that would necessitate treatment and disposal as a hazardous waste.