Mentor is the largest city in Lake County, Ohio, United States. The population was 47,450 at the 2020 census. It is part of the Cleveland metropolitan area. Mentor was first settled in 1797. In 1876, James A. Garfield purchased a home in Mentor, from which he conducted the first successful front porch campaign for the presidency; the house is now maintained as the James A. Garfield National Historic Site.