Multiferroic Bi_3.25La_0.75Ti₂Nb_0.5(Fe_1-xCo_x)_0.5O₁₂ ceramics with x = 0, 0.3, 0.4 and 0.5 were synthesized by a conventional solid-state reaction route to evaluate the effects of cobalt doping on structural, electrical and magnetic properties. All samples display layered perovskite Aurivillius phase with typical microstructure of plate-like grains. The grain size decreases with increasing Co content, from ∼5 μm to ∼1 μm. Room-temperature dielectric permittivity values range from 160 (x = 0) to 210 (x = 0.5) with negligible frequency dispersion and losses below 0.02 in a wide frequency range. A decrease of the Curie temperature with Co addition was observed. The Co-doped ceramics display well-defined ferroelectric and ferromagnetic hysteresis loops at room temperature. The best magnetic properties are obtained for x = 0.3 and x = 0.4 with a remnant magnetization of ∼0.1 emu/g. Butterfly-type hysteresis loops are observed for the magnetodielectric response using a measurement protocol that can be useful for other single-phase multiferroic materials. The MD coefficient does not depend on frequency and the maximum value (∼0.5%) is obtained for cobalt content x = 0.3. So, these multiferroic three-layer Aurivillius compounds may be considered as promising candidates for memory applications.