The largest known object in the universe is a structure called the Hercules-Corona Borealis Great Wall. It is a massive filament-like structure composed of galaxies and galaxy clusters. The Hercules-Corona Borealis Great Wall was discovered in 2013 and stretches over a distance of about 10 billion light-years, making it one of the largest known structures in the observable universe. However, it is important to note that the universe is vast and continually expanding, so there may be even larger structures yet to be discovered.