Population growth is driven by two factors: net migration (people moving in minus people moving out) and natural increases (births minus deaths). Since 1960, most growth in Thurston County has been due to immigration. Between 2000 and 2010, an average of 3,500 people moved to Thurston County per year (77% of total growth). While much of this immigration was likely due to the relatively stable economy in Thurston County, it is likely that the increasing cost of living in the Seattle metropolitan area played a role as well, as individuals from the metropolitan area looked for ways to reduce escalating costs of living, particularly in housing.
Immigration since 2010 has slowed to 1,900 new residents per year. It also accounts for a smaller proportion of total growth (63%).