Taken from the church's own website
The horned bull's head on the east end of the chancel is an unusual feature to find on a church, as horns are more generally associated with the devil. It would seem that the church had the horned bull before the town was called Hornchurch, as the first written reference, in 1222, refers to 'monasterium cornutum' or 'horned church/monastery' at Havering. The first reference to the horns on the east end of the church is in 1610 when they were said to be made of lead. When they were repaired in 1824 they were found to be of copper. It is reasonable to suppose they had been replaced during the intervening 200 years, but neither mentions the stone head, merely the horns. There are numerous legends and theories to explain their existence and whilst the truth may remain obscure the head forms a unique feature of the church.
In 1999 the copper horns were stolen from the bulls head. The horns are priceless and were never recovered. The Horns were replaced in 2001 allowing Hornchurch to live up to its name.