The Greenwich Country Day School is a co-educational, independent day school in Greenwich, Connecticut, United States, founded in 1926. As of 2019, it enrolled some 1190 students from nursery to 12th grade level. In November 2017, Greenwich Country Day acquired The Stanwich School, making it the only independent nursery through 12th grade co-educational school in Greenwich. The Head of School of GCDS is Adam Rohdie. The head of the high school is Chris Winters, former Greenwich High School principal.

It is accredited by the State of Connecticut through the New England Association of Schools and Colleges and is a member of the National Association of Independent Schools. The school is located on a rolling campus set into a series of hills. The Old Church Road campus is divided into three distinct schools, and the Upper School is on a separate campus on Stanwich Road. The two campuses are separated by less than two miles.