This lost church stood at the corner of Fish Street Hill and Eastcheap. The first mention of St Leonard Eastcheap was in 1177 in the reign of King John. In John Stow’s survey of London he says it was called St Leonard Milke Church after the builder William Melker:
“Up higher on this hill is the parish church of St. Leonard Milke church, so termed of one William Melker, an especial builder thereof, but commonly called St. Leonard’s in East Cheape, because it standeth at East Cheape corner. Monuments there be of the Doggets, namely, Walter Dogget, vintner, one of the sheriffs, 1380; John Dogget, vintner, and Alice his wife, about 1456; this John Dogget gave lands to that church; William Dogget, etc.”
The church does not appear on the Agas or Copperplate maps of 1555 but is shown on the Faithorne and Newcourt map of 1658. We have some idea of what it looked like as it appears on the Wyngaerde Panorama of 1543 where we see its tall spire. In 1618 the church was so badly damaged by fire that the steeple and the west end of the church had to be rebuilt. On Hollar’s panoramas showing London before and after the Great Fire, we can see St Leonard Eastcheap although it is not labeled as such. See the illustrations below.
The church was nor rebuilt after the fire and was combined with St Benet Gracechurch. When that church was demolished in 1868, it was merged with All Hallows Lombard Street which was demolished in 1937. So it finally ended up with St Edmund King and Martyr. Today the church of St Edmund King and Martyr includes the parishes of St Mary Woolnoth, St Nicholas Acons, All Hallows Lombard Street, St Benet Gracechurch, St Leonard Eastcheap, St Dionis Back Church and St Mary Woolnoth Haw. The long list is a testament to the large number of lost churches in the City.
You can still find traces of St Leonard Eastcheap today. There is a blue plaque on the corner of Eastcheap. There are two parish boundary markers – one in Pudding Lane and one in Gracechurch street showing the boundary with St Benet Gracechurch. Also if you visit the City of London Cemetery in Ilford you will find a tomb where the remains of the graveyard were reburied when the Metropolitan railway was built in 1882. See below.
The wikipedia page for St Leonard Eastcheap is here