We report a study of the La_1−xCe_xFeSiH solid solution (0 ≤ x ≤ 1), a family of intermetallic hydrides of ZrCuSiAs-type structure, with space group P4/nmm. For low cerium concentrations x ≤ 0.20, we observe the presence of superconductivity, which originates from the correlated 3d electrons of iron. The superconducting regime is progressively suppressed by the cerium substitution. For moderate cerium concentration 0.07 ≤ x ≤ 0.50, we observe evidence of the single-ion Kondo effect and no magnetic phase transition down to 2 K. For 0.07 ≤ x ≤ 0.20, the single-ion Kondo effect coexists with a superconducting ground state at low temperatures. From x > 0.50, we observe signatures of Kondo coherence and a heavy Fermi liquid regime at low temperature. Finally, at high cerium concentration x ≥ 0.85, we observe signatures of magnetic ordering at low temperatures. We discuss our results by introducing temperature scales related to superconductivity, the Kondo effect, and magnetic order, which permits building a rich phase diagram temperature versus cerium content x. This shows that using the cerium concentration x as a unique control parameter, we can explore the Kondo entanglement between correlated 3d and 4 f electrons, which suggests an unusual change between the superconducting state related to the 3d electrons and the Kondo coherent state involving both 3d and 4 f electrons.