Previous studies on the kagome ferromagnet Co3Sn2S2 have reported many controversial results. By using a variety of experimental studies, primarily neutron scattering, we have comprehensively solved the magnetic Hamiltonian, which is dominated by one in-plane nearest-neighbor interaction J, containing a Heisenberg component and a giant antisymmetric Dzyaloshinskii-Moriya Interaction (DMI), which is roughly 1/3 of J, and a small interplanar coupling. This giant DMI value is the largest reported in any system. The Hamiltonian results in a canted (noncollinear) ferromagnetic ground state with the umbrella-type R-3m′ structure, and our experiments provide evidence that this single structure is the true ground state at all temperatures below Tc with constant canting angle. This canted ferromagnetic structure may be the physical origin of the giant anomalous Hall effect previously reported rather than the Weyl nodes lying 60 meV above the Fermi level. Furthermore, this giant DMI may account for the chiral phonons detected in this compound.