Terry, the Chelsea and England captain, has denied making a racist remark to QPR defender Ferdinand.
Police have now confirmed their dealings with the complaint have moved on and a formal investigation has been launched.
The move means the Football Association's own investigation into the allegation cannot be completed until the outcome of the police probe.
Whether the latest development will have any impact on Terry's selection for England's two friendlies against Spain and Sweden later this month remains unknown.
A Metropolitan Police spokesman said: "Police were notified of an incident on Sunday October 23 involving alleged racial abuse. This is currently being investigated by officers from Hammersmith and Fulham."
The incident was alleged to have taken place during QPR's 1-0 win over Chelsea. Terry has denied racially abusing Ferdinand, insisting his own response was actually a denial and not racist in any way.
Terry, who has had a turbulent 18 months off the pitch, could find himself losing the England captaincy for the second time in his career if he is found guilty of racially abusing a fellow footballer on the pitch.
The FA said they will make no further comment until the police investigation is completed.
An FA statement said: "Further to an allegation from the recent QPR versus Chelsea fixture, the Football Association has been formally investigating the matter.
"The Metropolitan Police has contacted the FA to make us further aware of their investigation into the matter.
"Due to this it would be inappropriate for the FA to comment until the Police have completed their own enquiries.
"Therefore, the FA will make no further comment at this time."
Meanwhile, Ferdinand has been targeted with racist abuse via his Twitter account after releasing a statement saying he had "strong feelings" on the matter and backed the FA's inquiry.
On Tuesday, Ferdinand retweeted messages of support sent to him - but also a shocking racist jibe at him from someone who appeared to be a Chelsea fan.
Ferdinand has submitted an account of his exchange with Terry to the FA, and said in a statement: "I have very strong feelings on the matter, but in the interests of fairness and not wishing to prejudice what I am sure will be a very thorough inquiry by the FA, this will be my last comment on the subject until the inquiry is concluded."