Four new uranyl phosphonate compounds have been synthesized via ionothermal flux in the ionic liquids 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-ethyl-3-methylimidazolium bromide ([Emim][Br]). [C₈H₁₅N₂][UO₂(C₆H₅PO₃H)(C₆H₅PO₃)] ([Bmim][UPhPO]), [C₈H₁₅N₂]₂[(UO₂)₄(C₆H₅PO₃)₃Cl₄] ([Bmim][UPhPOCl]), [C₈H₁₅N₂][UO₂(HO₃P(CH₂)₃PO₃)] (α-[Bmim][UC₃DPO]), and [C₆H₁₁N₂]₂[(UO₂)₂(p-C₆H₄(PO₃H)₂)₃]·2H₂O ([Emim][UPhDPO]) form one-dimensional chains, two-dimensional sheets, or three-dimensional frameworks. For comparison, analogous reactions were carried out hydrothermally, which lead to one new framework structure, [C₈H₁₅N₂]₂[(UO₂)₅(HO₃P(CH₂)₃PO₃)₄] (β-[Bmim][UC₃DPO]), and one previously characterized tubular uranyl phosphonate. It was found that the structure is equally dictated by the choice of flux method, the choice of ligand, and the choice of ionic liquid.