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We investigated the magnetic and magnetocaloric properties of Gd_100-xCo_x (<inline-formula> <math display="inline"> <semantics> <mi>x</mi> </semantics> </math> </inline-formula> = 40 to 56) thin films fabricated by the sputtering technique. Under an applied field change <inline-formula> <math display="inline"> <semantics> <mrow> <mi>Δ</mi> <mi>H</mi> <mo>=</mo> <mn>20</mn> <mo> </mo> <mi>kOe</mi> </mrow> </semantics> </math> </inline-formula>, the magnetic entropy change <inline-formula> <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mo>Δ</mo> <msub> <mi>S</mi> <mi>m</mi> </msub> <mo stretchy="false">)</mo> </mrow> </semantics> </math> </inline-formula> decreases from 2.64 Jkg⁻¹K⁻¹ for <inline-formula> <math display="inline"> <semantics> <mi>x</mi> </semantics> </math> </inline-formula> = 44 to about 1.27 Jkg⁻¹K⁻¹ for <inline-formula> <math display="inline"> <semantics> <mi>x</mi> </semantics> </math> </inline-formula> = 56. Increasing the Co concentration from <i>x</i> = 40 to 56 shifts the Curie temperature of Gd_100-xCo_x (<inline-formula> <math display="inline"> <semantics> <mi>x</mi> </semantics> </math> </inline-formula> = 40 to 56) thin films from 180 K toward 337 K. Moreover, we extracted the values of critical parameters <i>T</i>_c, <i>β</i>, <i>γ</i>, and <i>δ</i> by using the modified Arrott plot methods. The results indicate the presence of a long-range ferromagnetic order. More importantly, we showed that the relative cooling power (RCP), which is a key parameter in magnetic refrigeration applications, is strongly enhanced by changing the Co concentration in the Gd_100-<i>x</i>Co<i>_x</i> thin films. Our findings help pave the way toward the enhancement of the magnetocaloric effect in magnetic thin films.