Tansy (Tanacetum vulgare L.) is an aromatic medicinal plant whose use is limited by the presence of toxic thujone. This research aimed to evaluate the morphological and chemical properties of tansy plants growing in various natural habitats. The research determined the content and chemical composition of the essential oil, the contents of flavonoids and phenolic acids, and the antioxidant activity levels of methanol extracts from tansy inflorescences. The highest amount of essential oil (1.05 mL·kg−1) was found in the raw material collected from the reclaimed area (R). Forty-seven compounds were identified in tansy oil, among which camphor (31.21–1.27%) and trans-chrysanthenyl acetate (76.09–0.09%) dominated, while the concentration of trans-thujone was low (2.67% on average). The highest amounts of flavonoids (0.52%) were found in the raw material collected from the ruderal (W) and reclaimed (R) sites, while the highest amount of phenolic acids (2.42%) was found in the raw material from the ruderal site (W). Tansy inflorescence extracts showed high antioxidant potential (88.41%). The reasons for the variability of the chemical composition of tansy were environmental and genetic variability factors