It depends. Under both the federal Divorce Act and the Ontario Family Law Act, a parent may be required to pay child support, even after a child turns 18, depending on whether certain statutory tests are met.
Under the Divorce Act, a “child of the marriage” includes offspring over the age of 16 who are still pursuing education, usually post-secondary education. This expanded definition is reinforced by the federal Child Support Guidelines, which allows for support to be paid for a child over 18 in full-time school attendance.
Under the Family Law Act, “child” includes an adult child, over the age of 18, who has not voluntarily withdrawn from parental control, and who is enrolled in a full-time program of education.
Whether or not your child meets these tests will depend on the circumstances.
For further information, see our article titled When Does Child Support Stop in Ontario?