The first egg was spotted by Derby Cathedral Peregrine Project web cam watcher, Justin Walker at 7.30 am on Saturday 18th March.
The falcon will now leave her egg on its own and is expected to lay three more eggs with two day gaps between each one, making a complete clutch of four. Once the third or fourth egg is laid, she will begin incubation.
Peregrines have been nesting on the cathedral tower since 2006 and the famous Derby peregrine webcams enable viewers to watch them live.