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.
Addington consisted of the northern and eastern portions of the merged county. Originally, it contained Ernestown township, Camden township, Sheffield township, Denbigh, Abinger and Ashby township, and Kaladar and Anglesea township. It now consists of the lower-tier municipalities of Addington Highlands, Stone Mills, and Loyalist.
There is a great deal of confusion about Addington as a municipality and Addington as an electoral district. As an electoral district, and indeed as a census division, the term Addington was and is applied to take in areas outside of the municipality, such as Kennebec township in Frontenac county. Thus, as an electoral district and as a census division, Addington included people who never paid taxes in Lennox and Addington County, nor voted for representation on County Council.
Therefore, Lennox and Addington elected separate representatives to the Parliament of Canada for many years.