It is located in the eastern portion of Southern Ontario.

The county of Frontenac, situated within the Mecklenburg District, was originally created as an electoral district for the Legislative Assembly of Upper Canada in 1792 and its original limits were described as being: bounded on the east by the westernmost line of the county of Leeds, on the south by Lake Ontario, to on the west by the easternmost boundary of the late township of Ernestown, and on the west by the easternmost boundary of the township of Fredericksburgh, running north twenty-four degrees west until it meets the Ottawa or Grand River, thence descending the said river until it meets the northwesternmost boundary of the said county of Leeds.

[3] At the beginning of 1800, the County was reorganized as follows:[4] Through the addition of newly surveyed townships, by 1845 the County covered the following territory: the Townships of Bedford, Barrie, Clarendon, Hinchinbrooke, Kingston, Kennebec, Loughborough, Olden, Oso, Portland, Pittsburgh, which shall include Howe Island, Palmerston, Storrington, and Wolfe Island, and, except for the purposes of representation in the Legislative Assembly, the Town of Kingston.

The county council itself was abolished and replaced by a management unit with limited powers, known as the Frontenac Management Board.

[1] Children attend schools part of the Limestone District School Board, based in the City of Kingston.