We report angle-resolved photoemission spectroscopy (ARPES) studies combined with $\mathrm{DFT}+\mathrm{DMFT}$ calculations to confirm that the magnetic ordering vector transition from $\mathrm{Q}=(1/2,0,0)$ to $\mathrm{Q}=(1/3,0,0)$ in the metallic triangular antiferromagnets ${\mathrm{Co}}_{1/3\pm \epsilon }{\mathrm{TaS}}_2$ ($\epsilon \approx 0.007$) is induced by the electronic structure change in the system. The ARPES-measured Fermi surface (FS) maps of ${\mathrm{Co}}_{0.325}{\mathrm{TaS}}_2$ show two hexagonal and one circular holelike FSs around $\mathrm{\Gamma }$, which matches well with the triple-Q state by taking into account the contribution of nesting vectors occurring between Co $3d$ and Ta $5d$ orbitals. In the case of ${\mathrm{Co}}_{0.340}{\mathrm{TaS}}_2$, a new electron pocket around K appears, and the FS geometry changes as a result of the correlation effect of ${\mathrm{Co}}_4{\mathrm{S}}_{18}$ tripods forming in the system. The magnetic susceptibility calculations based on the charge-self-consistent $\mathrm{DFT}+\mathrm{DMFT}$ band structures and the random phase approximation indicate that the most stable magnetic ordering vector (1/2,0,0) split into (1/6,0,0) and (1/2,0,0), which is consistent with the magnetic phase transition around $x=1/3$ in ${\mathrm{Co}}_x{\mathrm{TaS}}_2$.

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• Electronic structure
• Fermi surface
• Magnetic phase transitions
• Magnetism
• First-principles calculations
• Photoemission spectroscopy