The Pākehā population grew rapidly in the mid-19th century, firstly because of migration and then through high fertility rates. The Māori population declined throughout the 19th century until the early 1890s, when it began to grow again. 

The impact of the post-Second World War baby boom is particularly evident in the significant growth of the Pākehā population until the early 1970s. The Pacific population grew steadily from the mid-1960s, and was overtaken by the Asian population in the early 2000s.

Standard ethnic definitions have changed. Until 1976 Māori ethnicity was determined by the 'degree of Māori blood'. This changed to 'descent' in 1976 and back to 'blood' in 1981. 'Affiliation' was adopted in 1986 – people chose to identify themselves with particular ethnic groups. This remained the standard definition in the 2000s.