The authors report on the crystal and magnetic structure determination of ThFe₁₁C_x. The positions of the metal atoms correspond to the BaCd₁₁ type of structure. The carbon atoms occupy octahedral sites formed by four iron and two thorium atoms. Compounds having carbon concentrations x=1.5 and 2 were found in order magnetically between 400 and 500 K. Low-temperature neutron diffraction experiments provide evidence of a ferromagnetic structure with moments oriented perpendicular to the c axis whereas at room temperature the magnetic moments appear to be aligned parallel to the c axis of the tetragonal structure.