The most used verb in the English language is “be.”
Corpus studies typically rank the verb be—including forms such as am, is, are, was, were, been, and being—as the most frequent English verb. It works as a main verb, as in “They are happy,” and as an auxiliary verb in constructions such as “She is running” and “The work was finished.”
Its frequency comes partly from grammar: English uses be to describe identity, states, location, and existence, and to build continuous and passive forms. This makes it much more common than ordinary action verbs. The verb also has an unusually large set of forms, which can make it less obvious when counting occurrences.
A common mix-up is choosing have or do, which are also extremely frequent primary verbs and auxiliaries. Say is among the most common lexical verbs, especially in reported speech, but it does not generally outrank be when all grammatical forms and auxiliary uses are counted. Exact rankings can vary by corpus, dialect, register, and whether individual forms or the entire verb lemma are measured.