Union Chapel, Islington
Building From 1799
From Union Chapel: "Our story ... started in 1799 when dissenting congregants from St Mary’s, Upper Street began worshipping together in a private house in Highbury Grove." This was number 18. "Every year, we note our Foundation Day, 28 August, when worship began in the chapel that previously occupied this site, in 1806. The houses either side were built at the same time." The picture shows the site at this time. More information and pictures at the Friends page.
The current 1874-7 building is by James Cubitt (apparently unrelated to the various other architects and engineers with the same surname that were developing London at the same time, or so distantly related that it doesn't count) with additions in 1877-90.