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Webster 1913 Edition

Noun.

Readiness to believe on slight evidence; credulity.

Beyond all credulity is the

credulousness

of atheists.

S. Clarke.

Noun.

Credulity; easiness of belief; readiness to believe without sufficient evidence.

Beyond all credulity is the credulousness of atheists, who believe that chance could make the world, when it cannot build a house.

credulousness ‎(uncountable)

The characteristic or state of being credulous; credulity.
- 1911, Ernest Jones, "The Psychopathology of Everyday Life", The American Journal of Psychology, vol. 22 no 4 (Oct), pp. 525-6,
  Credulousness is always more harshly judged than incredulousness, though they are both merely different aspects of the same fundamental failing, namely, lack of true scepticism.

“credulousness” in An American Dictionary of the English Language, by Noah Webster, 1828.
credulousness in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913
“credulousness” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006.