We present the magnetic properties of the metal‐organic framework {[CoCxAPy]∙2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4`‐azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D‐coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two‐leg ladders with Co dimer rungs, running parallel to the c‐axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six‐coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single‐ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]∙1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard‐axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g‐tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a τlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built‐up of Co‐dimers with an anisotropic exchange interaction.