Lennon was shot outside the couple's Dakota Building apartment in New York on December 8, 1980, and Ono admits she and his sons still struggle with the untimely death of their beloved husband and father.
"After 39 years, Sean, Julian and I still miss him," she wrote on Twitter. "The death of a loved one is a hollowing experience."
She went on to call on American politicians to change U.S. gun laws, adding, "Every day, 100 Americans are shot and killed with guns. We are turning this beautiful country into a War Zone. Together, let's bring back America, the green land of peace."
She also shared a statistic that revealed over 1,400,000 people have been killed by guns in America since Lennon's death.