The primary population centres are Georgetown and Acton. Additionally, there are a number of hamlets and rural clusters within the town, including Ashgrove, Ballinafad (straddling the boundary with Erin), Bannockburn, Crewsons Corners (straddling the boundary with Erin, Guelph-Eramosa and Milton), Glen Williams, Henderson's Corners, Hornby, Limehouse, Mansewood, Norval, Scotch Block, Silver Creek, Speyside, Stewarttown, Terra Cotta (straddling the boundary with Caledon), and Wildwood. The area was first settled in the 1820s.
Halton Hills is located in the transition zone between the Huron-Ontario Forest Section of the Great Lakes-St. Lawrence forest zone to the north and the Niagara Section of the Carolinian forest zone to the south. Both forest zones are part of the Mixedwood Plains Ecozone. The natural vegetation in the Huron-Ontario Section is dominated by mixed wood forests. It is a transitional type between the southern deciduous forests and the northern coniferous forests. The forest communities of the Niagara Section are dominated by broad-leaved trees. Overall, Halton Hills consists predominantly of agricultural lands with scattered woodlands and wetlands. The woodlands are mainly deciduous forest and the wetlands are either cedar swamp or cattail marsh.
