Residents living in 55 homes in the Horwich End area of Whaley Bridge have been allowed to return to their properties.
Derbyshire police said the homes - which were evacuated on Saturday - are no longer in danger after the water level at Toddbrook Reservoir was lowered by nine metres.
But Deputy Chief Constable Rachel Swann said the dam still posed "a significant risk" to properties which were evacuated on Thursday, forcing 1,500 residents to flee their homes.
DCC Swann said: “Since Friday the Toddbrook Reservoir water level has been lowered well below that required for engineers to be able to access, and survey, the damage to the interior dam wall.
“It is my very happy duty to announce that the residents of the 55 homes in the Horwich End area of Whaley Bridge will be able to return to their properties tonight.
“While this is obviously good news for those residents there are many hundreds that are unable to return to the area.
“The dam wall still poses a significant risk to the properties that were evacuated on Thursday. Without a full assessment of the structure I am not able to be given the assurances I need to be able to say the threat to life has been eliminated.
“I am fully aware of the concerns that residents have and their wishes to get back to normality.
“You have my promise that as soon as it is safe - as we have shown today – we will get you home as quickly as possible.”
Residents returning to their homes are able to do so via the B5470 Chapel Road and the B5470 Macclesfield Road, which have been reopened.
They were reminded to remain aware of the danger posed by the dam and, should there be a failure, emergency service vehicles will sound their horns three times and a loud hailer will also sound.
Rail operator Northern also announced this evening that services on the Hope Valley Line between Sheffield and Manchester will recommence on Wednesday morning, but services between Buxton and Hazel Grove remain suspended until further notice.