In 1968 Middlesbrough became part of the County Borough of Teesside .
In 1974 Middlesbrough became part of the non-metropolitan county of Cleveland until the county 's abolition in 1996 , when Middlesbrough became a unitary authority .
In 1968 Middlesbrough became part of the County Borough of Teesside , and in 1974 it became part of the non-metropolitan county of Cleveland until the county 's abolition in 1996 , when Middlesbrough became a unitary authority .