The magnetic system of the pseudobinary compound Mn1-xCoxGe has been studied using small-angle neutron scattering and susceptibility measurements. It is found that Mn1-xCoxGe orders magnetically at low temperatures in the whole concentration range of x[0/0.9]. Four different states of the magnetic structure have been found at low temperatures: the long-range-ordered (LRO) short-period helical magnetic structure at x<xc1≈0.25, with helical wave vector ks≃2nm-1; the short-range-ordered (SRO) short-period helical magnetic structure at xc1≤x≤xc2≈0.45; the long-period helical magnetic structure at xc2<x≤0.8, with helical wave vector ks1nm-1; and the ferromagneticlike structure at x≈0.9.