Lilia Valutyte was found at the scene in Fountain Lane at around 6.20pm on Thursday, Lincolnshire Police said.
It comes after two people were arrested as part of a murder investigation following the “isolated incident”, the force said on Friday morning.
Later in the afternoon, Chief Superintendent Kate Anderson said: “Our thoughts continue to be with Lilia’s family and friends.”
The senior officer had described the nine-year-old’s death as an “utter tragedy”.
Lilia’s parents have been informed and are being supported by specially trained officers.
Those who wish to leave flowers and tributes can leave them at the corner of Fountain Lane and Fountain Place, it was said.
Ms Anderson had earlier declined to confirm Lilia’s nationality or comment on the details of those arrested and what they were detained on suspicion of.
At the scene late on Thursday night, a police car was stationed either side of an alleyway to cordon the area off to the public.
Two forensic officers in white suits could be seen working at the scene before leaving in the early hours of Friday.
The leader of Boston Borough Council Paul Skinner said: “The town is united in mourning following the very sad and tragic death of a nine-year-old girl in Boston.
“We can’t for one second imagine the pain the family and the young girl’s friends are going through and our heartfelt condolences go out to them.”
He added that the council will fly a flag from the Municipal Buildings at half-mast.
Matt Warman, the Conservative MP for Boston and Skegness, said he had been in contact with the policing minister to ensure national assistance is available to the murder investigation.
Writing on Twitter on Thursday evening, he said: “Profoundly shocking news in Boston this evening.
“I have spoken to senior officers locally and am hugely grateful for all the emergency services’ work.
“I have also been in contact with policing minister Tom Pursglove to ensure that any national help that might be useful is made available as quickly as possible.”