Lennox and Addington County is a county and census division of the Canadian province of Ontario. The county seat is Greater Napanee. It is located in the subregion of Southern Ontario named Eastern Ontario.The two original counties of Lennox and Addington, joined together in 1860, had been named after Charles Lennox, 3rd Duke of Richmond and Henry Addington, 1st Viscount Sidmouth, respectively.