Olive mill wastewater (OMW) was obtained during the extraction of olive oil. It is typified by an elevated concentration of sugars, acids, proteins, polyphenols, and organic matter. This makes the removal of OMW problematic for all olive oil-producing countries. Due to their high concentration in polyphenols, these wastewaters are a source of danger to the environment. This research aimed to study the spatial distribution effect in terms of geographical origin production of olive oil on the phenolic content and the antioxidant activity of the OMWs. A chemometric approach using principal component analysis (PCA) and hierarchical cluster analysis (HCA) was utilized. Physico-chemical characterization of OMWs was performed to evaluate their pollutant load by setting the following parameters: pH, dry matter, conductivity, and chemical oxygen demand. Quantitative analysis of the phenolic compounds shows that the extract of all samples had a high content of phenolics varying from 238.26 ± 5.67 to 534.16 ± 3.83 mg GAE/g of extract, flavonoids varying from 179.89 ± 1.64 to 421.47 ± 3.42 mg QE/g of extract, and tannins varying from 101.66 ± 0.65 to 216.28 ± 3.41 mg CE/g of extract. Antioxidant activity was determined by two testing systems: DPPH and ABTS assay. The IC50 DPPH varied from 0.30 ± 0.08 to 1.93 ± 0.34 µg/mL, while it varied between 2.04 ± 0.16 and 6.11 ± 0.25 µg/mL for the IC50 ABTS method. The principal component analysis indicated that the two methods DPPH and ABTS are strongly correlated. Furthermore, important correlations were shown by the principal component analysis (PCA) on the one hand between the phenolic compounds and on other hand between their antioxidant activities (DPPH, ABTS).