The confirmation of his departure from Blackburn comes after a day of claiming alongside Lancashire, his third victory in 12 league games.
Although only 11 points were obtained from 36 potential points since late December, Rover has maintained its place between high fires.
His last match in the Rover Cast was the FA Cup on Sunday against the Premier League wolves.
This is the second time in many seasons that Justas leaves a club while they are in the qualifying places at the championship table.
Although this step is under his own will, he spent his time in Birmingham suddenly ended in October 2023 by new owners, Win Rooney, the official.
It was a decision that sparked Blues sliding in the table, which reached its peak to the league later that season.
Blackburn was suffering from a problem declining themselves when Istas took the job in Iuud Park, and after keeping it, he directed them from among the hope of this term.
Derby, which lasted 10 games in all competitions – which included seven defeats in a row in the league – runs fourth from the bottom of the table and at the risk of an immediate return to the first league.
Eostace had two talismans in Derby as a player, as he spent the first to help the rams avoid the decline in the second layer in 2008-2009 while on loan from Watford.
He moved to PRIDE Park in a permanent deal in 2013 and saw the last two years of his play.
In that second talisman, he helped them reach one victory in the English Premier League, with Rams being hit in the QPR qualifying final in 2014.