Residents of Aamjiwnaang First Nation were not included in Sarnia's population during the 2016 census.
Mayor Mike Bradley shared the information Monday when some councillors appeared concerned that the city's growth rate dropped 1.1% to 71.594 last year.
"There's 600 to 700 people who are within the City of Sarnia, who aren't in that census report," says Bradley. "It distorts that census report."
Bradley says it's also difficult to derive the number of homeless individuals and students.
Population data is used by staff to help analyze the city's fiscal fitness plan and set upcoming budgets.
The plan focuses on the continued reduction of debt, increasing reserves, maintaining service levels, infrastructure renewal and maintaining reasonable tax rates.
The 2018 draft budget will be presented to council November 6, with a full day set aside for final budget deliberations on December 5.
