The Octagon Church was built in 1840 as a memorial to Lucy Yule (d. 1838) who was buried on the Mission Grant land at Middle Swan.  The Chapel was designed by her husband, the Resident Magistrate, Mr. T. N. Yule and her father, Dr. J. C. Harris.  It was officially opened on the 29th of November 1840 in the presence of His Excellency the Governor, John Hutt Esquire (who laid the foundation stone in 1839). ​

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In November 1848, Bishop Short of Adelaide, made his first visit to the western side of his diocese.  It was then that he consecrated this church.  He wrote the following in his diary:
Further on we came to the property of the Colonial Church Society  and called upon the missionary, Mr. Mitchell.  I inspected his chapel,  an octagonal building, neat and clean.  It was completely filled,  about 80 of the settlers having collected, though in the midst of  harvest.  The sun was setting with the clear, soft glow of the  beautiful climate when the congregation slowly separated.  I slept in  the house of the excellent pastor, the Rev. W Mitchell.  Simple,  faithful, self-denying, he labours without enjoying any of those  comforts which his age would seem to demand.

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The Octogon Church began deteriorating and the first section of St. Mary’s Church was built.  The old church was demolished circa 1871, long gone but not forgotten.  A picture can be viewed in the bottom panel of the ‘Pentecost’ stained glass window in the south transept of St. Mary’s.