According to the Oxford English Corpus, the most commonly used noun in English is “time.” In the OEC’s part-of-speech rankings, it appears ahead of “person,” “year,” “way,” and “day.”
This result comes from a very large collection of English texts, including books, newspapers, academic writing, websites, blogs, emails, and other material. The corpus contains more than two billion words, so its ranking reflects broad written usage rather than the vocabulary of one particular genre.
A common source of confusion is that “time” can function as both a noun and a verb, as in “time the race.” The ranking separates the noun use from other grammatical uses. The overall word-frequency list also places “time” at number 55, but that is a ranking among all word forms, not just nouns.
Corpus rankings are not universal laws of English: results can change with region, date range, spoken-versus-written material, and lemmatisation rules. Within the OEC ranking named in the question, however, “time” is the definitive answer.