Which city is located at the mouth of Eighteenmile Creek?

The city located at the mouth of Eighteenmile Creek is Olcott. Eighteenmile Creek is a significant waterway in the Niagara County region of New York, flowing into Lake Ontario near Olcott. This area is known for its picturesque waterfront and recreational opportunities, making it a notable destination for locals and visitors alike.

The other locations mentioned do not correspond to Eighteenmile Creek. Dexter is situated further inland and is not associated with this waterway. Kingston, located in Ontario, Canada, is at the confluence of the St. Lawrence River and Lake Ontario, quite distant from Eighteenmile Creek. Grimsby is a town in Ontario, Canada, and is also unrelated to this particular creek. Thus, the geographical relationship of Olcott with Eighteenmile Creek clearly makes it the correct answer.