Wallen was born in Hoxton and married Mary Ann Sydney (1828–1899) at Guildhall in 1848.
Millwall British School was built by James and Jonathan Coleman of Bermondsey in 1846–47.
[5] William won an allegedly corrupt competition to design the Vestry Hall at the Greenwich Public Offices.
William Wallen the younger of Lawrence Pountney Lane, in the City of London, Architect, Surveyor, Builder, Dealer and Chapman was declared bankrupt on 25 March 1854.
[6] William (jnr) was again declared bankrupt on 29 September 1869, but an Order of Discharge was granted on 10 December 1869.