Born in 2980 3A, Mosco was the eldest son of Milo and Peony Burrows. When the Ruffians invaded the Shire on September 5, 2990 3A, Mosco, along with his brother Moro Burrows and newborn sister Myrtle remained hidden and protected while their parents were enslaved. However on October 5, an open revolt happened when Gandalf arrived to put a stop to the Ruffians.
When Sauron was preparing for war against the free people of Middle-earth, Mosco was tasked by his parents to take care of his siblings while they left with the Shire Company. Mosco really wanted to go, but his mother convinced him to do stay and take care of the family. After the war ended, Mosco and his siblings were devastated for their parents' death. Together, they arranged a funeral for those that perished after the war ended.