Clutha's population has increased 0.3% in the past seven years, significantly boosted by the Otago Corrections Facility near Milton.
Census figures released this week show the Bruce area (near Milton, Waihola, and Taieri Mouth) saw an increase of 444 people, up from 2658 in 2006 to 3102, while the township of Milton has also increased from 1887 to 1929.
The Otago Corrections Facility at Milburn was opened in 2007, and has a capacity of 485 prisoners.
When contacted by the Otago Daily Times, a Statistics New Zealand spokesman confirmed prisoners were included in census figures.
Clutha Mayor Bryan Cadogan said that while prisoners might have boosted the district's population, prison staff also contributed to Clutha's growth.
He said it was hard to get a real feel from figures, but he had felt for some time that the district was growing.
''I'm thrilled to see we've arrested the decline and from here on up we're moving forward.''
Overall, the district was up 51 people, increasing from 16,839 in 2006 to 16,890.
Mr Cadogan said population was always one of his key focuses, and he believed youth were the key to boosting Clutha's development.
''I believe it starts with attracting the youth to stay in the district. We need to maximise the potential of our youth. The true reversal of the trend will be when the youth see the district as the best place to live. It will take time, but they are our future.''
Further south, the population of the Gore district has declined by 0.6% since 2006, dropping from 12,108 to 12,033.
Gore Mayor Tracy Hicks said it was disappointing to see the population decline, particularly when he felt the district was growing.
''We felt we had arrested the decline and were looking for some growth. It has reinforced in my mind ... that in the next few years we really need to see the council place population at the top of the agenda.''
Mr Hicks said the council needed to put time and effort into creating an environment to encourage growth as the South already offered a lot in terms of lifestyle.
