Gait is a complex motor task, initiated and governed by different areas of the brain. Studies have shown a clear association between gait and cognition. Impairments in both gait and cognition are prevalent in older adults. Older adults with gait impairment have an increased risk of developing cognitive impairments. Those with cognitive impairment often have gait impairments and more falls than cognitively healthy older adults. Recent studies have shown that quantitative gait analysis, particularly performed during dual task conditions, can detect gait deficits that cannot yet be seen by the naked eye, even to a trained specialist. Some studies have shown that such gait disturbances were measurable years before mild cognitive impairment or dementia or walking difficulties were clinically manifest. Quantitative gait analysis can provide early detection of gait and cognitive impairments as well as fall risk. Future quantitative gait studies may help distinguish dementia subtypes in early stages of the diseases. Early detection of gait and cognitive impairments would provide a better understanding of disease pathophysiology and progression. Early detection also allows the timely implementation of interventions with the ultimate goal of improving or maintaining mobility and functional independence for as long as possible. Quantitative gait analysis should be viewed as a clinical tool to aid diagnoses and treatment planning. This review examines the current literature on quantitatively measured gait impairment in older adults with mild cognitive impairment or a dementia subtype.