The populations of both Mountain View and Red Deer counties dropped slightly between 2006 and 2011, according to federal census numbers released last week.Red Deer County's population went down by 1.6 per cent – or 298 people – from 18,649 in 2006 to 18,351 in 2011.While the census figures for Mountain View County showed a 0.4 per cent increase – from 12,308 in 2006 to 12,359 in 2011 – the 2006 numbers were disputed and revised by a county census conducted in 2007, which pegged the population at 12,570.As a result, Mountain View County's population is down by 211 people, or about 1.7 per cent.Annexation was identified by both county administrations last week as the leading factor driving the decrease.“Between the last census and this one every single municipality in the county has gone through an annexation process,” Red Deer County manager Curtis Herzberg said.“It was part of ensuring the urban municipalities had their room to grow and agreements between us and them for intermunicipal lands were there.”The seven municipalities – City of Red Deer, Sylvan Lake, Delburne, Elnora, Penhold, Innisfail and Bowden – all had increases in population, with Sylvan Lake and Penhold seeing the largest boost by 20.3 per cent and 20.5 respectively.Mountain View County CAO Tony Martens also said annexation was the main reason for the population decline, although county staff had not yet analyzed the new census figures last week.Corporate services will be reviewing housing starts and other indicators to determine if the census results are indeed accurate and whether it's in the county's interests to again conduct its own census, Martens said.“We need to go to council and say we either recommend a census or don't recommend a census.”With many provincial grants based on population, the difference can have an effect on the county's bottom line – but those potential benefits have to be weighed against the cost of conducting a census, Martens added.In contrast, towns within Mountain View County saw across-the-board increases in population, with Carstairs experiencing the largest growth at 27.5 per cent, followed by Didsbury at 15.1 per cent, Olds at 13.5 per cent and Sundre at 3.4 per cent. The Village of Cremona saw a 1.3 per cent decrease.For both counties, increased population counts in partnering urban municipalities will mean a change in per-capita funding for shared services, but Herzberg said he expects the impact will be minor.“I think it is fair to say there would be a small, small reflection in the changes in the numbers based on this,” Herzberg said.“Just like any community involved within a particular partnership, if their numbers have gone up we'll see a small shift.”The 2011 census figures for municipalities within Red Deer County sit at 90,564 for Red Deer, 12,327 for Sylvan Lake, 830 for Delburne, 313 for Elnora, 2,375 for Penhold, 7,876 for Innisfail and 1,241 for Bowden.Within Mountain View County, the new population counts are: 8,235 for Olds, 4,957 for Didsbury, 3,442 for Carstairs, 2,610 for Sundre and 457 for Cremona.In surrounding counties, Clearwater's population rose by 3.8 per cent to 12,278, Rocky View went up by 9.9 per cent to 36,461 and Kneehill's population dropped by 5.7 per cent to 4,921.