We present results on the hydrothermal growth of ($\text{L}{{\text{i}}_{1-x}}\text{F}{{\text{e}}_{x}}$ )OHFeSe single crystals using floating-zone-grown ${{A}_{x}}\text{F}{{\text{e}}_{2-y}}\text{S}{{\text{e}}_{2}}$  (A  =  K, Rb, and Cs) as precursors. The growth proceeds by the hydrothermal ion exchange of Li/Fe–O–H for K, Rb, and Cs, resulting in a stacking layer of ($\text{L}{{\text{i}}_{1-x}}\text{F}{{\text{e}}_{x}}$ )OH sandwiched between the FeSe layers. Optimal growth parameters are achieved using high quality A 0.80Fe1.81Se2 single crystals added to the mixtures of LiOH, H2O, Fe and C(NH2)2Se in an autoclave and subsequently heated to 120 °C for 2 d, to obtain highest quality single crystals. The obtained crystals have lateral dimensions up to centimeters, with the final size related to that of the precursor crystal used. All ($\text{L}{{\text{i}}_{1-x}}\text{F}{{\text{e}}_{x}}$ )OHFeSe single crystals show a superconducting transition temperature T c  >  42 K, regardless of the phase of the precursor such as superconducting K0.80Fe1.81Se2 (T c  =  29.31 K) or non-superconducting Rb0.80Fe1.81Se2 or poor-superconducting Cs0.80Fe1.81Se2 (T c  =  28.67 K). The T c and transition width ΔT vary in the obtained single crystals, due to the inhomogeneity of the ionic exchange. X-ray diffraction analysis demonstrates that the 245 insulating phase is absent in the ion-exchanged single crystals, while it is observed in the ${{A}_{x}}\text{F}{{\text{e}}_{2-y}}\text{S}{{\text{e}}_{2}}$  precursors. Comparative studies of the structure, magnetization, and superconductivity on the parent A 0.80Fe1.81Se2 and the ion-exchanged ($\text{L}{{\text{i}}_{1-x}}\text{F}{{\text{e}}_{x}}$ )OHFeSe crystals are discussed. A phase diagram including antiferromagnetic spin density wave and superconducting phases is also proposed.