What is the object of a preposition?
The object of the preposition is the noun that follows the preposition, the word that the preposition relates to another word in the sentence. It can also be a pronoun, gerund, infinitive, or noun phrase.
The car is in the garage. (in is the preposition, and garage is the object of the preposition.)
We went to the grocery store for milk. (the grocery store is the first object of a preposition; milk is the second object of a preposition.)