Aust-Agder was a county (fylke) in Norway until 1 January 2020, when it was merged with Vest-Agder to form Agder county. In 2002, there were 102,945 inhabitants, which was 2.2% of Norway's population. Its area was 9,212 square kilometres (3,557 sq mi). The county's administrative center was the town of Arendal.

Vest-Agder was one of 18 counties (fylker) in Norway up until 1 January 2020, when it was merged with Aust-Agder to form Agder county. In 2016, there were 182,701 inhabitants, around 3.5% of the total population of Norway. Its area was about 7,277 square kilometres (2,810 sq mi). The county administration was located in its largest city, Kristiansand.