Met Office figures showed the region saw 363mm (14.3in) of rain, which is 105mm more than the previous record for the region in 1993.
The figures also show it was the most unseasonably warm December since 1910.
Across England, average temperatures reached 9.4C (49F), a rise of 4.3 degrees on the year before.
It was in stark contrast to the sub-zero temperatures recorded in 2010, the coldest since records began.
The unseasonably warm weather even saw trees blossom and flowers bloom, while attractions such as the ice rink at the Tower of London were forced to close.
9.4C (49F)
2015 was the warmest since 1910
-0.4C (31.3F)
2010 was the coldest recorded
1934 7.5C (45.5F)
1974 7.3C (37.4F)
1988 6.9C (44.4F)
1953 6.6C (43.9F)
Flooding caused by Storm Desmond brought record breaking rainfall to parts of England, such as the Lake District. And the UK overall recorded the wettest calendar month since 1910. Storm Frank also saw homes flooded across the North of England and Scotland.
England had its wettest December in three years with 137mm (5.4in) of rain. However it was only the 12th wettest on record. The wettest English December was 1914 with 179mm (7in) of rain. And 2012 was a much wetter December than 2015 with 148.9mm (5.9in).
137mm (5.4in)
of rain in England, December 2015
1914 was wettest, 179mm (7in)
1915 168.4mm (6.6in)
1929 165.5mm (6.5in)
1933 was driest, 21.5mm (0.85in)
Storm-ravaged north-west England saw record-breaking rainfall in December, some 40% higher than the previous record.