Francis Blomefield was born in the village of Fersfield in the south of the English county of Norfolk on 23 July 1705. The eldest son of Henry Blomefield (described by the Norfolk historian Walter Rye as "a gentleman of independent means"), and his wife Alice, the daughter and heiress of John Batch, of Lynn. He was educated at the grammar schools at Diss and Thetford. In April 1724 he was admitted to Caius College, Cambridge, where he graduated with a Bachelor of Arts degree in 1727 and a Master of Arts degree in 1728. On leaving university in 1727, he was ordained a priest, appointed Rector of the Norfolk parish of Hargham in 1729, and shortly afterwards Rector of Fersfield, his father's family benefice in the county. On 1 September 1732, he married Mary Womack, the daughter of a former rector of Fersfield. They had three daughters, two of whom survived into adulthood.