My Great (x3) grandfather, John McLoughlin, lived in John Street in 1841 (Court 6, House 4). Close by lived my Great (x3) great-uncle (?), Roger Moraghan (writted as Morgan on the census) who lived at Court 6, House 5. My great (x2) grandfather, James Moraghan from County Roscommon, appears to have left Roscommon at the height of the famine in the early 1840's to live with Roger and his family in John Street. James married John McLoughlin's daugher, Ann, in 1850 at St. Chads Cathedral and on the 1851 census they are shown as living at Court 6, House 4 John Street (Morgan, rather than Moraghan, on the census). On the 3rd April 1854 James and Ann had their first child, Henry, who was born at Court 6 John Street. John McLoughlin died in 1849 and my Great (x3) grandmother, Mary McLoughlin, was shown as living at House 2, Court 10, John Street. On the 1861 census Mary is shown as now living at House 5, Court 11 John Street and on the 23rd January 1867 Mary died in Court 5, John Street of chronic bronchitis.
Sadly, Roger Moraghan (aka Morgan) and his family moved from John Street to Court 1, Steelhouse Lane where he died in 1871. The reason I use the word 'sadly' is that Court 1, Steelhouse lane was even worse than John Street and it also appears in the same book by Robert K Dent (mentioned at the beginning of this thread).
Court 1, Steelhouse Lane
View attachment 134754
There's a very good 1750 map of Birmingham by Samuel Bradford which shows John Street following on from Newton Street ...
http://mappingbirmingham.blogspot.com/2012/06/1750-map-of-birmingham.html
1750 Map of Birmingham