Background: This study aimed to use item response theory (IRT) to explore the item-by-item characteristics of a mild cognitive impairment (MCI) screening tool using community-based data. Methods: The Yilan Study is a community-based study that has been conducted since 2012. Until March 2020, 2230 older adults were interviewed according to the household registration data. IRT was applied to determine the item-by-item distinctive characteristics of the Eight-item Interview to Differentiate Aging and Dementia (AD8). Results: The MCI characteristics in the AD8 items have varying degrees of item response threshold. In all circumstances, item AD8-8, which is related to self-rated memory ability, had a low item response threshold. AD8-5 and AD8-7, which are related to the comparisons of time-oriented functional status, had slightly lower thresholds, especially for those aged 65–79 years or without activity limitations. Conversely, AD8-1, AD8-2, AD8-3, AD8-4, and AD8-6 had similar item response thresholds and discriminative power; these items have more detailed functional descriptions or examples for illustration. Conclusions: Concise and understandable elements are often expected in community-based screening tools. For community-based health screening and population empowerment in the early detection of MCI, assessment tool items with detailed functional descriptions and examples for illustration have similar validities in most of the population. Items related to self-rated memory ability might be less valid. More examples may be needed for items constructed for comparing time-oriented functional status, especially in extremely old adults and individuals with activity limitations.