The largest structure in the Universe is a Quasar Group 4 billion light-years wide.
Jared Sperli stashed this in space
The largest known structure in the universe has been discovered by an international team of astronomers. The large quasar group (LQG -a portion shown above)) is so large that it would take a vehicle traveling at the speed of light some 4 billion years to cross it. Quasars are the nuclei of galaxies from the early days of the universe that undergo brief periods of extremely high brightness that make them visible across huge distances. These periods are 'brief' in astrophysics terms but actually last 10-100 million years. Since 1982 it has been known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes, forming large quasar groups or LQGs.
4 billion light years is roughly a quarter the size of the known universe, right? Wow.