1530s, "action, a thing performed, anything done, a deed," good or evil but in 16c.-17c. commonly "evil deed, crime;" from Latin factum "an event, occurrence, deed, achievement," in Medieval Latin also "state, condition, circumstance" (source also of Old French fait, Spanish hecho, Italian fatto), etymologically "a thing done," noun use of neuter of factus, past participle of facere "to do" (from PIE root *dhe- "to set, put").
An earlier adaptation of the Old French word that also became feat. The older senses are mostly obsolete but somewhat preserved in such phrases as after the fact, originally legal, "after the crime." Also compare matter-of-fact.
The modern, empirical, sense of "thing known to be true, a real state of things, what has really occurred or is actually the case," as distinguished from statement or belief, is from 1630s, from the notion of "something that has actually occurred." The particular concept of the scientific, empirical fact ("a truth known by observation or authentic testimony") emerged in English 1660s, via Hooke, Boyle, etc., in The Royal Society, as part of the creation of the modern vocabulary of knowledge (along with theory, hypothesis, etc.); in early 18c. it was associated with the philosophical writings of Hume. Middle English thus lacked the noun and the idea of it; the closest expression being perhaps thing proved (c.1500).
Hence facts "real state of things;" in fact "in reality" (1707). By 1729, fact was being used of "something presented as a fact but which might be or is false."
By fact is also often meant a true statement, a truth, or truth in general ; but this seems to be a mere inexactness of language .... Fact, as being special, is sometimes opposed to truth, as being universal ; and in such cases there is an implication that facts are minute matters ascertained by research, and often inferior in their importance for the formation of general opinions, or for the general description of phenomena, to other matters which are of familiar experience. [Century Dictionary]
Facts of life is by 1854 as "the stark realities of existence;" by 1913 it had also acquired a more specific sense of "knowledge of human sexual functions." The alliterative pairing of facts and figures for "precise information" is by 1727.
Facts and Figures are the most stubborn Evidences; they neither yield to the most persuasive Eloquence, nor bend to the most imperious Authority. [Abel Boyer, "The Political State of Great Britain," 1727]
Facts are stubborn things is in an 1822 translation of the popular novel "Gil Blas" (earlier English translations have facts speak for themselves).
"consisting of or pertaining to facts, not fanciful or ideal," 1712, from the noun phrase matter of fact "reality as distinguished from what is fanciful or hypothetical, truth attested by direct observation or authentic testimony," which is originally a legal term (1570s, translating Latin res facti), "that which is fact or alleged fact; that portion of an inquiry concerned with the truth or falsehood of alleged facts, subject of discussion belonging to the realm of fact" (as distinguished from matter of inference, opinion, law, etc.). See matter (n.) + fact.
The meaning "prosaic, unimaginative, adhering to facts" is from 1787. Related: Matter-of-factly; matter-of-factness. German Tatsache is said to be a loan-translation of the English word.
In law, that which is fact or alleged as fact; in contradistinction to matter of law, which consists in the resulting relations, rights, and obligations which the law establishes in view of given facts. Thus, the questions whether a man executed a contract, and whether he was intoxicated at the time, relate to matters of fact; whether, if so, he is bound by the contract, and what the instrument means, are matters of law. [Century Dictionary]
Factoids ... that is, facts which have no existence before appearing in a magazine or newspaper, creations which are not so much lies as a product to manipulate emotion in the Silent Majority. [Mailer, "Marilyn," 1973]
By 1988 it was being used in the sense of "small, isolated bit of true factual information."