Father's Day
Father's Day was not celebrated in the US, outside Catholic traditions, until the 20th century. As a civic celebration in the US, it was inaugurated in the early 20th century to complement Mother's Day by celebrating fathers and male parenting.
After Anna Jarvis' successful promotion of Mother's Day in Grafton, West Virginia, the first observance of a "Father's Day" was held on July 5, 1908, in Fairmont, West Virginia, in the Williams Memorial Methodist Episcopal Church South, now known as Central United Methodist Church. Grace Golden Clayton was mourning the loss of her father, when in December 1907, the Monongah Mining Disaster in nearby Monongah killed 361 men, 250 of them fathers, leaving around a thousand fatherless children. Clayton suggested that her pastor Robert Thomas Webb honor all those fathers.
Mother's Day
The modern Mother's day began in the United States, at the initiative of Ann Reeves Jarvis in the early 20th century. This is not (directly) related to the many traditional celebrations of mothers and motherhood that have existed throughout the world over thousands of years, such as the Greek cult to Cybele, the Roman festival of Hilaria, or the Christian Mothering Sunday celebration (originally a commemoration of Mother Church, not motherhood). However, in some countries, Mother's Day is still synonymous with these older traditions.