The £1.5 million record signing reached that milestone by setting the play-off chasers on the way to a 2-0 victory over Gillingham at London Road.
Assombalonga broke the deadlock four minutes before the break when beating Gills goalkeeper Stuart Nelson with a smart finish following a knock-down from recalled full-back Kgosi Ntlhe.
Nelson was also powerless to prevent skipper Tommy Rowe doubling the Posh lead in 58th minute with a rasping 20-yard drive which crashed in off the underside of the bar.
Assombalonga should have added another six minutes later when earning a penalty after being brought down by Bradley Dack, but his spot-kick was kept out by Nelson, who made a series of fine saves.
But fluffing his lines from 12 yards didn't stop Assombalonga from receiving high praise from his manager.
Ferguson said: "Britt has had a hell of a season. To have 30 goals by this stage is incredible.
"He has been absolutely fantastic for us and he is going to be some player. There is still so much to come from him.
"His opening goal was very important because people were getting a bit frustrated. It can be very difficult to play against a team who only want to sit behind the ball as Gillingham did first half.
"We were then very dominant in the second half when they opened up more. My attacking players did very well and the only disappointment is that we didn't score more than two goals."
Victory leaves Posh in a strong position to clinch the final Sky Bet League One play-off spot. They are six points clear of closest challengers MK Dons with five matches remaining.