Lilley is set in the bosky, bucolic Chiltern Hills, between Luton and Hitchin. The A505, which follows the route of the old Icknield Way, is just to the south, while the new Icknield Way long-distance path is just to the north.
Preserved in the church are pictures of the old church, which was of 12th century origin; we can see that it had typical late medieval windows and a feeble-looking tower, possibly weather-boarded, and Hertfordshire spike. On the north it had some Early English lancet windows, which are echoed in the new design. It was deemed to be in such bad repair that restoration was impossible. The vicar, the Rev. Arthur Coles Haviland (d.1904), who arrived in the parish in 1868, set about raising the funds for a new one. It probably helped that he was independently wealthy. He raised £3600 (about £438,000 today, which would scarcely buy you a three bed semi there nowadays), and in 1870 commissioned Thomas Jeckyll (1827-81) to build him a new church (and rectory and school). The result was, as often happened (compare Barley and Therfield, for example), something much grander than might be expected in a medium-sized village.
Jeckyll was an important figure in the Aesthetic Movement of the later 19th century; he was responsible (with James McNeill Whistler) for the famous Peacock Room of 1876-77, originally designed for a townhouse in Kensington but now in the Freer Gallery in Washington DC. However, I don't think that anyone who was previously unaware of this connection could possibly deduce it from the church, which is in most respects a fairly standard Gothic Revival church in the Victorians' favourite early Decorated style (i.e. imitating buildings of c.1300).
Stepping into the porch under the tower we find that it's built of brick inside, and that there are several monuments from the old church.