美国驻日陆军（英语：United States Army, Japan，USARJ；日语：在日米陆军／ざいにちべいりくぐん），同时为驻日美军中的陆军单位、及美国太平洋陆军的下属司令部，管辖美国陆军派遣日本的部队、附属单位、相关雇员及2,000名美国陆军官兵，在本州岛、冲绳使用数个后勤基地及港口设施，并与日本陆上自卫队进行联合演习、培训及发展相关计划，在东亚维持一支有效的威慑性武力，。部设在神奈川县的座间基地。

驻日陆军及设在座间基地内的美国陆军第1军前方司令部（I Corps (FWD)）负责支持美日安保条约中第五条（Article V，视对日攻击为共同危险）、第六条（Article VI，地域安全之维持）的落实，因此驻日陆军司令部担任美国陆军前沿部署部队的指挥单位及管制总部、与日自卫队支持地区安全活动、并提供美国在日军人、雇员及眷属优良的住所和作战设施。

United States Army, Japan (USARJ) consists of about 2,000 soldiers and is charged, during peacetime, with operating port facilities and a series of logistics installations throughout Honshū and Okinawa. USARJ participates actively with the Japan Ground Self-Defense Force in bilateral training exercises and the development of bilateral plans. It commands and supports United States Army assigned units, attached units, and augmentation forces and employs these forces in support of the commander. USARJ maintains and strengthens the credibility of deterrent power in the Pacific through maintenance of defense facilities, war reserves and operational project stocks. USARJ is headquartered at Camp Zama.