  In this work, we present detailed $^{57}$Fe M\"ossbauer spectroscopy
investigations of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ compound
to study its possible magnetic structures. We have shown that the previously
reported magnetic structures can not satisfactorily describe our low
temperature M\"ossbauer spectra. Therefore, in combination with theoretical
calculations, we have proposed a modulated helicoidal magnetic structure that
can be used to simulate the whole series of our low temperature M\"ossbauer
spectra. Our results suggest that the combination of previously reported
different magnetic structures are only approximations of the average magnetic
structure from our modulated helicoidal model. We anticipate that the proposed
modulated non-collinear magnetic structure might shed light on the
understanding of the complex magnetoelectric effects observed in this system.
