In Cornwall the word "Lan" originally meant "monastery", but often simply came to mean "church".   This fine Cornish church, at the head of a wooded valley, was originally a chapel established and maintained by the Augustinian priory at Launceston; it belonged to St.Stephen.   It was then a simple Norman building with a narrow nave, chancel, sanctuary and transepts, and cruciform in shape.   The original font remains, with deeply chiselled circles and heads at the corners representing the four evangelists.   Various additions were made in the Middle Ages, including the construction of the south aisle in 1436, when  the lofty tower was also completed and consecrated.

That year also saw the instigation of the graveyard, as before then the inhabitants had to use the cemetery at St Stephens-by-Launceston, eight miles away - a situation that caused much complaint.

The church is jointly dedicated to St Sidwell and St Gulval.   St Sidwell (or Sativola) was a female saint from Exeter, both names being corruptions of the Old English "side-fulla", meaning "full of purity".   She was adopted by the Launceston priory.  The dedication to St Gulval is obscure, with a theory that it may simply be a mistake - Laneast being confused with Lanestly, an alternative name for the parish of Gulval, near Penzance.

Late medieval stained glass includes part of a crucifixion in the east window and in the south chancel window St. Christopher and the Christ child keep company with St Etheldreda of Ely.  She is identified by her crown and abbess`s crosier.  The presence of an East Anglian princess here could be due to pilgrimage links with East Anglia or a sense of sisterhood among female royal saints.

Perhaps the best known of the memorials within the church is the polished black marble plaque in memory of the famous Cambridge University astronomer John Couch Adams, who discovered the planet Neptune.   He was born at Lidcott, within the parish, and died in 1892.  

The fine wagon roof with a roof boss of a crowned female head, assumed to be the patron St Sidwell,is found in the chancel.   A prayer desk with rose and arms of the Prior of Laynceston (a cockerel) on one side and a Lily vase (for the Annunciation) with a lindworm or dragon over it on the other side.  The W with a line through it, above the Prior`s arms, may stand for William Hopkyn, prior of Launceston c.1491-1507.  (A similar prayer desk is at Coldridge in Devon dating 1511.)  The bench ends are of similar style to the prayer desk with symbols of the passion including dice. 

 The whole church "survived" Victorian restoration in 1848.

There are six bells, and the early 16th century pulpit was greatly reduced in height and placed in its present position in 1900.   John Wesley, the founder of Methodism, took a special delight in preaching from the Laneast pulpit, doing so on six separate occasions.