Ordnance Survey maps are reproduced with the permission of the National Library of Scotland from their Map images website. Other maps accessed via oldmapsonline.org, from David Rumsey Map Collection and British Library Online Gallery.
So far, these are the earliest maps I have found that show Mornington Road. A post office map of 1859 (and Reynolds map of the same year) show Mornington Road – but devoid of any buildings:
But this next one, Bacon’s 9 inch, compiled by Edward Waller and published in Weekly Dispatch, Jan 1861 to May 1862 shows the complete set of grand houses on the west side, and the county court, church and the short terrace on the east side, that is referred to by M F Elliston in A Topography of Tower Hamlets. (see History 1855-1900). One of the many interesting things on this map is the first Bow Road station, sited on the south side of Bow Road, on the bridge at the corner of Arnold Road.
1866 – Stanford’s composite map of London and its suburbs below has the east side with fields, not buildings except for the County Court at the junction with Bow Road.
In the OS 25 inch England and Wales, London XXVIII, Surveyed: 1870, Published: 1876, as in Stanford’s 1866 map above, the “unusually grand” houses on the west side of Mornington Road are shown extant, but the east side is pasture or garden with an unidentified building at the southernmost end. Unlike the previous maps, it shows the wall across the end of the street. The no. 4 in the empty land on the east side is a ‘parcel number’ in the Ordnance Survey Books of Reference, signifying in this case 1.076 acres of pasture. On this map the Presbyterian Chapel is shown entirely in Mornington Road, behind the County Court, with no frontage on Bow Road.
The first map I can find that shows a full complement of houses on the east is the Ordnance Survey Five feet to the Mile, 1893-1896, Sheet VII.50, published 1895. There are six houses in the centre shown with a different plan, with a porch or approach steps, which might suggest they were built at a different time to the terraces either side. The County Court and Presbyterian Chapel are clearly marked, as is the tramway in the centre of Bow Road: