Which planet was the first discovered with a telescope?

Uranus was discovered by William Herschel on 13 March 1781, making it the first planet found using a telescope. It had been observed before as a faint point of light, but not recognized as a planet. Herschel initially thought it might be a comet before its orbit showed it was a new planet. The discovery expanded the known boundaries of the Solar System for the first time in recorded history. Uranus remains a landmark in the history of astronomy.