St Mary Colechurch stood on the corner of Cheapside and Old Jewry and was founded sometime before 1176. The name “colechurch” is probably derived from the nearby charcoal market. Charcoal was much in demand from the metalworkers in next door Ironmonger Lane. A blue plaque on the corner of Old Jewry marks the spot where the church stood shown in the photo below.
The church belonged to the Hospital of St Thomas of Acre until the dissolution of the monasteries in 1538 by Henry VIII. The Mercers Company – whose hall is next door – rebuilt the church in 1570 and repaired the east window in 1638. Thirty years later, the church was destroyed in the Great Fire of London and not rebuilt.
The parish was combined with that of St Mildred Poultry, but the latter church has also been lost, demolished under the Union of Benefices Act in 1871. The churchyard was cleared and the human remains reburied in the City of London Cemetery in Manor Park. A monument in that cemetery marks the reburial site as shown in the photo below – the inscription is so worn I have had to enhance it digitally with black ink, but if you visit it yourself you can still just make out the lettering .
The only other physical remains of the church are some parish boundary markers like the one shown below in King Street which show the boundary line between St Martin Pomeroy and St Mary Colechurch.
The wikipedia page for St Mary Colechurch
The history of St Mary Colechurch from British History Online