Which Buddhist council included the conclusions that there is no creator-god and no day of judgment? After the Buddha is said to have achieved Nirvana, there were subsequent Buddhist Councils that were held. 

Some years ago I came across an article that said that it was in one of these Councils that it was made official for Buddhists that there is no creator-god and no Day of Judgment. Which council was that? I think it was the Fourth? But I just can't find that information again.
It is incorrect that this is later development. From the onset in the Buddhism teaching did not have the teaching of a Creator God or Judgement Day.

The Buddhist notion of a creator is the stained mind or conditioned mind or unliberated mind. We keep creating our next moment due to Kleshas. This is further explained in Dependent Origination and the Links of Dependent Origination. This is evident from the Udana 'Anekajati samsaram sandhavissam' in which refers to the creator as Ignorance.




  Aneka jati samsaram,
  Sandhavissam anibbisam;
  Gahakarakam gavesanto,
  Dukkha jati punappunam.
  Gahakaraka ditthosi,
  Puna geham na kahasi;
  Sabba te phasuka bhagga,
  Gahakutam visankhitam;
  Visankharagatam cittam,
  Tanhanam khayamajjhaga.
  
  -Udana uttered by the Buddha after His enlightenment.
  
  So many births I have taken in this world, seeking in vain the bui1der of this house; in my search over and over, I took new birth, new suffering.
  
  Oh! house builder, now I have seen you, you cannot make a new house for me; all your beams are broken, the ridge pole is shattered; my mind is freed from all the conditionings of the past, and has no more craving for the future.
  
  [ The 'house builder' referred to above is avijja (ignorance). 'house' or 'new house' referred to above is nama-rupa (the mind-matter continuum) which is infact the 5 aggregates (pancakkhanda)-matter or body (rupa) and the 4 parts that constitute the mind, consciousness (vinnana) perception (sanna), sensation (vedana), reaction or conditioning (sankhara).]
  
  This has been discussed in more depth later on under "cause-effect (paticca-Samuppada)".


Above extracted from http://www.buddhanet.net/bvk_study/bvk212a.htm