Who was on the throne in England in 1800 - 1900?

The king of England in 1800 was George III. He had become king in 1760 and was the king during the American Revolution. He married Charlotte of Mecklenburg-Strelitz and had a large family. His health declined and eventually his son became the regent of the county until his father died in 1820. George III was King of Great Britain, and seperately, King of Ireland from 1760 until 1800. On 1st January 1801 the crowns of Great Britain and Ireland were united and his title then became King of Great Britain and Ireland.

He was not "King of England" as there had not been a monarch with that title since 1707.