Oku (邑久郡, Oku-gun) was a district located in Okayama Prefecture, Japan.
As of 2003, the district had an estimated population of 39,365 and a density of 313.64 persons per km2. The total area was 125.51 km2.
瀬戸内市は、平成16年11月1日に牛窓町、邑久町、長船町が合併して誕生しました。