Sleep-wake cycle characteristics, such as sleep quality and quantity, are related to Alzheimer’s disease (AD) risk and progression. Specifically, density of sleep spindles, electric oscillations occurring in NREM Stage 2 sleep, has been associated with cognition and AD biomarker soluble protein levels. Similarly, hippocampal volume (HV) and integrity (HI), which are indirect markers of hippocampal health, have been demonstrated to be early indicators of neurodegenerative progression and AD risk. This study analyzed relationships between sleep spindle densities of varying frequency (fast and slow) and these hippocampal features to better understand how sleep spindles and the hippocampus interact in the preclinical stages of AD progression. Ninety-two cognitively normal elderly individuals completed nocturnal polysomnography, habitual home sleep assessment, actigraphy, MRI scans, and cognitive testing. Fast spindle density and HI were significantly positively associated, and there were positive associations between N2 total spindle density, HV, and HI. However, slow spindle density was not correlated with any hippocampal metrics. These findings suggest that there are important differences in how fast spindle and slow spindle oscillations are generated and associated with hippocampal health and memory processing, with a probable stronger functional connection between the hippocampus and fast spindles. Candidate mechanisms for the connection between fast spindles and the hippocampus include spindle-driven changes in dendritic plasticity and thalamocortical fast spindle triggering of sharp waves and ripples. These results indicate that fast spindles may have public health benefits as an unintrusive, cost-efficient and scalable AD biomarker to monitor AD progression and develop novel treatments that can delay AD onset. This is the first study to examine the relationships between N2 spindle densities and hippocampal volume and integrity (HPF) in humans.