Question: Thamesville, Ontario is located between Chatham and which city with a population of 383,822 people and is at the confluence of the Thames River?

Context paragraphs:
St. Marys, Ontario: St. Marys is a town in southwestern Ontario, Canada.  It is located at the junction of Thames River and Trout Creek, southwest of Stratford, surrounded by the Township of Perth South and located in Perth County, Ontario.  However, like Stratford, St. Marys operates under its own municipal government that is independent from the County's government.  Nonetheless, the three entities "enjoy a large degree of collaboration and work together to growth the region as a leading location for industry and people".  Census data published for Perth County by Statistics Canada includes St. Marys and most Perth County publications also do, at least in some sections of the document.

Oxoboxo River: The Oxoboxo River, shown on federal maps as Oxoboxo Brook, is a tributary of the Thames River in New London County, Connecticut.  It flows roughly 6 mi in a southeasterly direction from its source at Oxoboxo Lake to its confluence with the Thames.  It has a watershed of 6768 acre , 87% of which is in the town of Montville.

Ellice Swamp: Ellice Swamp is a large woodlot in Perth County, Ontario.  The swamp covers approximately 856 hectares (2,115 acres).  It is located between Stratford and Milverton in the northeastern portion of the Thames River Watershed, between the North Branch of the Thames and the Nith River.

Upper Thames River Conservation Authority: The Upper Thames River Conservation Authority is a body based in London, Ontario, Canada.  It was created in 1947.  It was responsible for the construction of the Fanshawe Dam, completed in the 1950s, to control flooding from the Thames River, which runs through London.  During the last ice age, the site of London was the terminus of a large glacier.  When the region warmed at the end of the ice age, the glacier melted and receded North, leaving behind a drainage ditch and features such as Sifton Bog.  As such, the Thames is a watershed for most of Western Ontario, and is therefore highly susceptible to seasonal flooding.  In 1937, such flooding had devastating consequences, destroying over 1,000 homes, and causing millions of dollars in damage.

Thamesville: Thamesville is a community in Chatham-Kent, Ontario, Canada.  It is located at the junction of former provincial Highways 2 and 21, between Chatham and London.  Its name comes from the Thames River that flows nearby and the suffix -ville.

Avon River (Ontario): The Avon River is a river in Perth County, Ontario, Canada.  The river was named after the River Avon in England when the town of Stratford was founded on its banks in 1832.  The Avon River rises northeast of Stratford and flows southwest, entering the North Thames River near St. Marys.  It was originally known as the Little Thames River.

Delaware, Ontario: Delaware is a community located about 10 km west of and outside of London, Ontario, Canada within Middlesex County.  Delaware straddles the Thames River.  Delaware is accessed by the old highway (Highway 2) linking London and Chatham and the freeway (Highway 402) linking Sarnia along with Port Huron and Toronto.

Medway Creek (Ontario): Medway Creek is a tributary of the Thames River in southwestern Ontario, Canada, draining into the North branch of the Thames at the University of Western Ontario.

London, Ontario: London is a city in Southwestern Ontario, Canada along the Quebec City–Windsor Corridor.  The city has a population of 383,822 according to the 2016 Canadian census.  London is at the confluence of the Thames River, approximately 200 kilometers from both Toronto, Ontario and Detroit, Michigan; and about 230 kilometers from Buffalo, New York.  The City of London is a separated municipality, politically separate from Middlesex County, though it remains the county seat.

Woodstock, Ontario: Woodstock is a city in Southwestern Ontario, Canada.  The city has a population of 40,902 according to the 2016 Canadian census.  Woodstock is the seat of Oxford County, at the head of the non-navigable Thames River, approximately 128 km from Toronto, and 43 km from London, Ontario.  The city is known as the Dairy Capital of Canada and promotes itself as "The Friendly City".

Supporting paragraphs: Thamesville London, Ontario
Answer: London