Like most villages in Cornwall, Sennen is named for the saint who founded the parish church, and like most Cornish villages the identity with the saint is quite strong (maintained by an annual commemorative Feast day, celebrated here on Advent Sunday) even if the identity of the saint himself is a bit vague.
Not much is known about St. Sennen. A St. Senan was born near Kilrush in Ireland in 488. He founded many churches there, and is supposed to have founded this church in 520. He could have visited here on his way to Brittany, where he is associated with Plouzane. Ireland became Christian long before other parts of the British Isles and Irish missionaries soon spread the faith into the Western Isles, Wales and Cornwall. St. Columba founded his monastery on Iona in 563, thirty four years before St. Augustine made it to Kent. Although the Irish Saints probably didn't make extended voyages on millstones and fig leaves they managed to cross the seas somehow to spread their message, perhaps travelling with fishermen and merchants.
The three parishes of Sennen St. Buryan and St. Levan have been linked one way or another for most of their history. King Athelstan re-founded the church at St. Buryan in 932 giving it a special 'peculiar' status as a Royal Deanery, to which the churches of Sennen and St. Levan were attached as chapelries, though in other respects they functioned as separate parishes. To the inhabitants of Sennen the most significant cause of disgruntlement with this arrangement was that despite being able to hear mass and marry in their own church they were not allowed to bury their dead around it. For this they had to make the tedious trip across country to St. Buryan, leaving their homes open to attack from sea-borne raiders while they were about it. (The Spanish were a nuisance into the sixteenth century). They sent a petition to Rome asking for a bishop to be sent to hallow the churchyard for burial. Pope Martin V read and dismissed their appeal on 21 February 1430. This was a bad year for Joan of Arc, too. She was captured and sold to the English, and burnt in 1431.
Trouble from the sea arrived 37 years later when Perkin Warbeck, the hapless 'White Rose of England' landed at Sennen Cove. By 1497 he was nearing the end of his botched career pretending to be Richard, Duke of York (the real one may or may not have been dead already). A few of the local fishermen joined his small force, perhaps they were still annoyed at the failure of the Cornish Rebellion which had come to an inglorious end a short while earlier, and marched with him to Exeter. It was a mistake. Warbeck was defeated again and imprisoned and the Sennen men let off lightly with a hefty fine.
By the time all this happened the church stood substantially as it is now. The nave, north transept and chancel date from the thirteenth century, the tower from the later fourteenth and the south isle from the fifteenth. This replaces an earlier transept for the original plan was cruciform. The porch is not mediaeval, and might replace an earlier one. The roof, pews and windows, except those of the tower, are all nineteenth century. These date from the restoration the church underwent shortly after the deanery of St. Buryan was abolished in 1864.
If you walk around the church before entering you will be able to see the blocked low side window, which once helped light the chancel, the blocked east window of the transept and a door in the north wall. This was known as the devil's door because it was left open during baptisms to allow the devil to escape after having been driven out of the child by the holy water. That is why it pays to be careful where you stand during a baptism, because the devil now only has one way out. The tall cross standing near the tower was brought to the churchyard in 1878 by a Rector who formed the notion that it would be a good idea to collect all the parish crosses together. Luckily he didn't succeed and was made to put them back where they came from. This one was obviously too heavy to move again.