[Purpose] The purpose of this study was to evaluate the lower limb muscle strength of the community-dwelling elderly, with or without cognitive decline, using isometric knee extension strength (IKES) and the 30-second chair stand test (CS-30). [Subjects] A total of 306 community-dwelling elderly participated in this study. Assessment items were the CS-30, IKES, Mini-Mental State Examination (MMSE), and Trail-Making Test Part A (TMT-A). [Methods] Participants were divided into three groups according to their MMSE score: cognitive impairment (MMSE ≤ 24), cognitive decline (MMSE 25 to 27), and normal (MMSE ≥ 28). We compared IKES and CS-30 among the three groups. [Results] IKES was not significantly different among the three groups. However, the CS-30 was significantly different among the three groups. Upon further analysis the CS-30 score of each group, when adjusted for age and TMT-A, did not indicate a significant difference. [Conclusion] These results suggest that the lower limb muscle strength of the elderly does not differ with cognitive decline. Moreover, we suggest that when using the CS-30 score as an indicator of lower limb muscle strength attentional function should be taken into account.