The County Borough of Teesside was a county borough in the north-east of England, which existed for just six years. It was created in 1968 to cover the Teesside conurbation which had grown up around the various port and industrial towns near the mouth of the River Tees. The council was based in Middlesbrough, the area's largest town. The county borough was abolished in 1974 on the creation of the new county of Cleveland, which covered a larger area, with the county borough's territory being split between three of the four districts created in the new county.

Middlesbrough is a town in the Middlesbrough unitary authority borough of North Yorkshire, England. The town lies near the mouth of the River Tees and north of the North York Moors National Park. The built-up area had a population of 148,215 at the 2021 UK census. It is the largest town of the wider urban Tees Valley area, which had a population of 678,400 in 2021.