The magnetic properties of the (Fe,Mn)₂(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP_1−xSi_x-system (0.00 ≤ x ≤ 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co₂P-type structure (x < 0.15) and the Fe₂P-type structure (0.24 ≤ x < 0.50). Certain compositions have potential for use in magnetocaloric applications.