Nanostructured Co-doped anatase TiO2 (Ti1-xCo xO2-δ) samples were prepared and studied with particular emphasis on their compositional, structural, and magnetic properties. A detailed microstructural analysis was carried out to investigate the nature of the Co incorporation into the anatase TiO2 matrix. By combining different techniques, we confirmed the replacement of Ti4+ by Co 2+ ions in the anatase TiO2 structure. Neither segregated secondary phases nor Co-rich nanocrystals were detected. Co doping was found to introduce oxygen vacancies into the system by means of a charge-compensation process. Superconducting quantum interference device magnetometry demonstrated paramagnetic Curie-Weiss behavior with antiferromagnetic interactions even in the presence of a high density of oxygen vacancies. The fitting of the M(H) curves in the limits of low and high temperatures enable the fractions of isolated and antiferromagnetically coupled Co ions to be extracted. 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