The influence of Ag-doping on the crystallographic structure, magnetic properties, and magnetocaloric effects of Mn1−xAgxCoGe (0.01 ⩽ x ⩽ 0.10) is reported. A transformation of crystal structure from orthorhombic to hexagonal was observed at room temperature. Doping Ag in Mn sites results in a first-order magnetostructural transition near room temperature. A Curie-temperature window of 90 K was obtained between the Curie temperatures of the austenite (Ni2In-type) and martensite (TiNiSi-type) phases. Large magnetic entropy change values of ~22.0 and 9.4 J/kg/K, and refrigerant capacity of 308 and 272 J/kg, were found for x = 0.06 and 0.05, respectively, for μ0ΔH = 5 T.