Mn₃Si₂Te₆ is a three-dimensional material with a trigonal unit cell that is structurally-related to the van der Waals bonded ferromagnetic semiconductors CrSiTe₃ and CrGeTe₃. In Mn₃Si₂Te₆, the filling of an interlayer octahedral position leads to three frustrated magnetic exchanges that result in a ferrimagnetic spin configuration. The magnetism has been investigated using thermodynamic and transport measurements on single crystals, first principles calculations, and neutron diffraction and diffuse scattering. A net moment exists due to an imbalance in the multiplicity of two different Mn sites, and an unexpectedly large anisotropy field of ≈9T is present at 2K. The 3^rd nearest neighbor exchange is stronger than the 2^nd nearest neighbor exchange. Frustration results in a relative suppression of the Curie temperature with T_C=78K compared to a Weiss temperature of -277K. As a result, short range correlations exist well-above T_C, as demonstrated via diffuse neutron scattering. This study has revealed complex magnetic behavior in Mn₃Si₂Te₆ and highlights the variety of states that may be accessible in this family of materials. This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.