Established 24 July 1788 as one of four districts within Upper Canada. Consisted of the area that is now the current counties Frontenac, part of Hastings, Lanark, part of Leeds, Lennox & Addington, Prince Edward, and Renfrew.

Renamed Midland District in 1792.

See Midland District for further information.

Mecklenburgh District was located in South-Eastern Ontario.