The September date was set by decree after a proposal from the Independent Election Commission, said government spokesperson Amadou Coulibaly.
Eleven members of the government will stand in the regional elections, according to a list published by the RHDP.
Prime Minister Patrick Achi will be seeking re-election as head of the Me regional council, his home area in the southeast.
The coming votes are considered a test of the strength of Ivory Coast's leading political groups before the presidential vote in the West African nation.
The elections will be a first outing for former president Laurent Gbagbo's new African People's Party - Ivory Coast (PPA-CI), a left-wing pan-African group.
Gbagbo returned to Ivory Coast in June 2021 after being acquitted by the International Criminal Court on human rights charges linked to post-electoral violence in 2011.
The governing RHDP party won control of 18 of the country's 31 regions five years ago, with the main opposition Democratic Party taking six.