Kirkby was mentioned in the Doomsday book in 1085, and it is quite certain that a church stood here in Saxon days. The present church of St Mary was built around 1802.
Although situated in a small rural Lincolnshire village, there is much documentation of St Mary’s. In a volume of a Lincoln Record Society entitled 'The state of the church’ by Canon Foster we are told that in 1602 ‘the church and the chancel are in very good repayre , and kept decently yet the Steple ys decaied'.
In 1640, Holles, the historian, states that he saw in the Rectory, a coats of arms in stained glass which were probably originally in the church. He also mentions two monuments in the chancel to the memory of the two Rectors, Richard Lambard and William Bullier, but these, with the glass have entirely disappeared. It seems that at that time, the church was richly furnished inside by the gifts of wealthy people living locally. And, more recently the villagers have again furnished the church, for in 1926 a stained glass window was installed at the east end as a War Memorial. The amount contributed exceeded all expectations and there was sufficient money to also put two single lights on either side, as well as, the central three light window. The glass is by William Morris and the subject The Resurrection. In the two smaller windows are figures representing Valor and Fortitude.