The claustrum is a thin grey matter structure that lies subcortically embedded between the external and extreme capsules, the putamen, and the insular cortex. In recent studies, the claustrum has been linked to cognitive control and, in particular, to cognitive flexibility in both animals and humans. Moreover, the claustrum has been reported to be involved in various aspects of sleep. In the present study, we explored resting-state functional connectivity of the claustrum in relation to both habitual sleep parameters and cognitive control performance in humans. Our aim was to explore the role of the claustrum in potentially mediating known interactions between cognitive control and sleep. Given the small size of the claustrum and the potential for partial volume effects, we followed a “Small Region Confound Correction” procedure where a “flanking mask” comprised of voxels surrounding the claustrum was regressed out from the whole-brain signal. Participants’ habitual sleep was quantified through actigraphy-based measures along consecutive days, while cognitive control performance was assessed at the lab through a task battery that included measures of inhibition, shifting (cognitive flexibility), and updating. Results show a distinct connectivity fingerprint for the claustrum, and significant claustro-frontal, claustro-parietal/occipital, and claustro-cerebellar associations with both sleep and cognitive control (cognitive flexibility and inhibition) that differed between the right and the left claustrum. These results expand on the view of the claustrum as being involved in cognitive control and habitual sleep in humans, and point toward a potential role of this structure in mediating interactions between sleep and cognitive flexibility.