Location from harry-potter-deathly-hallows by
The fallen government -- seized by Voldemort without a single curse fired, now home to the Muggle-Born Registration Commission and a propaganda machine wearing the mask of legitimate authority.
The Ministry fell three days after Dumbledore's death. Death Eaters walked in, sat at desks, and started writing new laws. Pius Thicknesse, the puppet Minister, signs whatever is placed in front of him. The Muggle-Born Registration Commission operates from the courtrooms where Death Eaters were once tried. Umbridge presides. Dementors guard the accused. Harry, Ron, and Hermione infiltrate the Ministry using Polyjuice Potion to steal Slytherin's locket from Umbridge. They impersonate three Ministry employees, navigate the building while it runs normally around them, and escape with the Horcrux after Harry stuns Umbridge in her courtroom and frees the Muggle-borns she was about to sentence. It is the most audacious thing they've done since breaking into Gringotts, which they haven't done yet.
Vast underground complex. The Fountain of Magical Brethren has been replaced by a monument showing wizards sitting on thrones of crushed Muggle bodies, inscribed 'MAGIC IS MIGHT.' Interdepartmental memos still zip overhead. Umbridge's courtroom on the lower levels. Everything looks the same. Everything has changed.
Also known as: the Ministry, Ministry of Magic