More than 600 family and friends are thought to have arrived so far.
Some 200 people packed into the church, which can seat 150, while more than 400 stood on the grass outside.
The Rev Emma Davies described Claire as a "truly beautiful" person who "sparkled".
We gather to remember Claire and to give great thanks to Claire who gave so much to so many people.
Donations made in memory of 30-year-old Claire Squires have broken the £1million mark on the same day her funeral has been announced.
The 30-year-old who died during Sunday's London Marathon has been called an "inspiration" and "incredible".
Donations to the charity of Claire Squires, the young woman who died in the London marathon, have reached almost £220,000.