The parish of Terrington St John lies in Norfolk's Fenland, the village is adjacent to the busy A47, which crosses Norfolk from east to west, and is roughly midway between King's Lynn and Wisbech (where it leaves the county to the west). This area is reclaimed land and lies barely above sea-level, the village main street (formally part of the A47 which now bypasses) is barely 3 metres above sea level. A landscape of wide open skies and a land dominated by agriculture with much market gardening on the silty soils. St John is one of two Terrington's in this area its namesake is, however, a little further to the north adjacent to the King's Lynn to Sleaford road.

St John's church lies slightly north of the present village of Terrington St John alongside the broad lane linking it to Terrington St Clement. It is an impressive Fenland church with a lofty tower which is visible for miles in the flat landscape. The church dates from the early 14th Century and there is much that is Perpendicular. The tower was once detached from the church, a Fenland tradition given the unstable ground, but has been connected with a covered passage. The church was much restored in Victorian times, like many Norfolk churches, but remains a landmark in the fenland scene.