There is a scholarly consensus that Shakespeare contributed about 1,800 words (and phrases) to the English language. Most of his lexical innovations were nouns (e.g., addition, assassination, bedroom, discontent, investment, luggage, moonbeam, pedant, radiance, watchdog, zany) and verbs (e.g., arouse, besmirch, donate, grovel, impede, negotiate, submerge, undervalue, widen) and adjectives (e.g., abstemious, bloodstained, deafening, equivocal, fashionable, jaded, lonely, obscene, sanctimonious, unreal). A few adverbs also figure as products of his inventiveness (e.g., abjectly, rightly, unaware, vastly). But he did not add one single preposition to the fifty or so which already existed in his time. As we have seen, they had been in existence for centuries. He made use of all of them, with a few exceptions (though some of these he employs as other parts of speech): alongside, across, amid(st), around, atop, inside, and outside. He never uses onto, a word first recorded in 1715.
In fact, as is the case with the English language in general, prepositions (together with articles, pronouns and conjunctions) are the most frequently used parts of speech. Of the first sixteen most frequently used words in Shakespeare, five are prepositions: after the (first place), and (second place), and I (third place) they are to (fifth), of (sixth), in (tenth), for (fourteenth) and with (sixteenth). Not a single noun, adjective or adverb appears in the first fifty of Shakespeare’s most frequently employed words, and only four verbs (be, have, do, are, as well as will if we realize it also gets counted as a noun).