Updated project metadata. Genes encoding the KDM5 family of transcriptional regulators are disrupted in individuals with intellectual disability (ID). To understand the link between KDM5 and ID, we generated five Drosophila strains harboring missense alleles analogous to those observed in patients. These alleles showed effects on neuroanatomical development, cognition, and other behaviors, in addition to a transcriptional signature that included the downregulation of many ribosomal protein genes. A similar transcriptional profile was observed in KDM5C knockout human glutamatergic neurons derived from induced pluripotent stem cells (iPSCs), suggesting a conserved role for KDM5 proteins in regulating ribosomal protein genes. Quantifying changes to the translatome caused by reduced KDM5 in Drosophila neurons, we find that the translation of mRNAs required for mitochondrial activity was particularly affected. Altered mitochondrial activity was confirmed through metabolomic studies that revealed decreased citric acid cycle activity. KDM5 therefore plays a key role in maintaining mitochondrial function that, when altered, could contribute to cognitive and behavioral phenotypes.