Just over half (53%) of all babies registered in 2011 were born to parents who were married or in a civil partnership, according to figures from the ONS.
The figure is a substantial drop from 1986 when the proportion was closer to 80%.
However, the number of births registered by sole parents (almost 6%) has fallen since 2001 while more parents are co-habiting (31%).
More top news
Russia will pay the price for launching air strikes to prop up the Assad regime, the US defence secretary has warned.
'Vote Leave' - a cross-party campaign calling for Britain to leave the European Union in the forthcoming referendum - has been launched.
Sir Bruce Forsyth had to be rushed to hospital after a fall at his home.