From the Wikipedia page 
Njombe Urban District is one of the six districts of the Njombe Region of Tanzania, East Africa. The administrative seat for the district is in the city of Njombe.
Njombe Urban District was formally established when it was gazetted in March 2012. It was created out of the south-eastern part of the old Njombe District that had been in Iringa Region. Western Njombe District became Wanging'ombe District, and the northern part became Njombe Rural District.