Addington County is a historic county in what is now the Canadian province of Ontario. It was named after Henry Addington, 1st Viscount Sidmouth. As an upper-tier municipality, the county of Addington was created on paper in 1792, but has never existed as a discrete municipal entity. From 1792 until 1864, it was part of the United Counties for Frontenac, Lennox and Addington. In 1860, permission was given by the Legislature for Frontenac County to separate. From 1864 until the present, Addington has been part of the united counties of Lennox and Addington.