Wycombe District Council's local plan, which was adopted in August last year, proposes building 13,200 new homes in its district by 2033.
The plan earmarks a 32-hectare site near the village of Bourne End, known as Holland Farm, for removal from the green belt and the construction of 467 new homes.
This was despite objections from local charity, Keep Bourne End Green.
The charity instructed a team of expert consultants to represent it at the plan's 2018 public examination, but a planning inspector confirmed the allocation of Holland Farm.
The plan, as it was submitted before January 2019, was based on the policies in the 2012 National Planning Policy Framework (NPPF) rather than the revised 2018 framework.
Keep Bourne End Green argued that that plan's housing target was based on a housing need calculation that relied on out of date 2014-based household growth projections from the Office for National Statistics (ONS).
Shortly after the public examination opened in 2018, the ONS published fresh 2016-based figures that predicted a growth in the number of households in the district of 6,350 by 2033, compared to the 2014-based projections of 10,990.
That represented a reduction in projected growth in the number of households in the district of 4,640, or about 42 per cent.
The charity argued that, had the up to date projections been taken into account, the outcome of the local plan process could have been very different.
Ruling on the case, Mr Justice Holgate said the inspector had put "a formal question" to the council during the examination process, asking whether the updated household projections represented "a meaningful change" in the district's housing situation.
The council - which was abolished in April this year and absorbed by unitary authority, Buckinghamshire Council - replied in the negative and asserted that the updated projections had no bearing on the "soundness" of the draft local plan.
In her report to the council, the inspector acknowledged that the projections indicated that household growth in the district had "slowed significantly."
However, she noted "some doubts about the reliability" of the 2016-based projections and the importance of boosting the overall supply of housing.
There was a public interest in certainty and reassessing housing need in the light of the updated projections would result in significant delay, the inspector added.
In court, Keep Bourne End Green argued that the allocation of the Holland Farm site was a result of the inspector and the council "erroneously rejecting" the updated projections as the "demographic starting point" for the assessment of future housing need.
The newer ONS projections were at the very least a material consideration which should have been taken into account.
The charity also argued that the inspector had been wrong to find "exceptional circumstances" justifying the release of Holland Farm from the green belt.
Dismissing the challenge, however, the judge said the inspector was "plainly entitled" to question the reliability of the newer ONS projections as a tool to be used in plan making.
The projections only provided a "starting point" for assessing housing need and the inspector was justified in citing the national policy imperative to boost the overall supply of new homes.
He added that the requirement in the 2012 National Planning Policy Framework to base local plans on up to date evidence is qualified by the words "wherever possible". Such evidence also need only be taken into account where it creates "a meaningful change in the housing situation."
ONS household growth projections are "not an expression of (housing) need", he said, and the weight to be given to them was a matter for the inspector's planning judgement. Her decision was properly reasoned and not irrational, he found.
Mr Justice Holgate also rejected the charity's argument that the inspector was wrong to find that there were exceptional circumstances justifying Holland Farm's removal from the green belt.
In her report, she described the appearance of the site as "semi-urban". It was, she said, a "sustainable location" for development and its removal from the green belt would not result in a significant loss of countryside.
Observing that there is "no requirement that green belt land may only be released as a last resort," the judge said: "General planning needs, for example general housing, are not excluded from amounting to exceptional circumstances."