Alzheimer's disease (AD) disrupts behavioral circadian rhythms, but its effects on molecular rhythms in the human brain are poorly understood. Using single-nucleus RNA sequencing (snRNA-seq) from post-mortem cortical samples, we informatically estimated the relative circadian phases of 409 persons with and without AD dementia, reconstructing circadian expression profiles across cell types. Although core clock rhythms were preserved in AD, many cell-type-specific circadian outputs were disrupted. Rhythms in ribosomal biogenesis and oxidative phosphorylation were dampened across cell types. Similar losses in ribosomal gene expression rhythms were observed in amyloid precursor protein/presenilin 1 (APP/PS1) mice, which showed further reductions in ribosomal protein expression and polysome-mediated translation after circadian desynchrony. Exploratory computational modeling reveals that altered translation may contribute to the increased circadian variability seen in AD patients. These findings reveal altered cell-type-specific circadian output rhythms in the brains of AD-affected patients and highlight disrupted ribosomal rhythms as a feature of AD.