Lily was built in 1889 by the London & Southwestern Railway's Nine Elm's Works under special order for the Wellsworth & Suddery Railway Company (later known as the Tidmouth, Knapford and Suddery Railway) and arrived at the same time as Adam to work with Colin. When the North West Railway was formed in 1914, Lily mainly handled the Arlesburgh Branch when it was built in 1916. In 1923, Lily was asked to cover for Henry on the main line when the big green engine was bricked up in the tunnel, and Colin took care of Lily's Branch Line. When Colin rammed some houses, Lily realized that if Henry hadn't indulged in the tunnel, she'd be on her own branch, and Colin would never had the accident, and her branch line wouldn't have to shut down for three days. This made Lily hold a grudge against Henry for the rest of her life.
Lily is undoubtedly a responsible, reliable, and really useful engine. She has a caring side too, and prides her work so much that she tends to dislike engines who were (or are) irresponsible. According to Gordon, she always has been a 'proper lady'.
Lily was painted in the W&S standard maroon and gold livery with black wheels and golden borders and stripes. She formerly had W&S written on her tanks and 2 on her bunker in gold, but nowadays it was replaced by NWR and 35.
Lily is based on an 0-4-4T 'LSWR O2 class' steam locomotive, designed for the 'London and South Western Railway' by 'William Adams'.
- In Mistrust, her theme is Emily's from the Thomas and Friends TV series.
- A new shed was given to Lily in Season 2 of Sodor: the Modern Years at the Ffarquhar Branch Line Sheds, which was made by WildNorWester.
- Lily was originally developed as STEY/STMY's answer to 'Lady' from Thomas and the Magic Railroad. This can be seen in her name and livery, as well as her backstory.
- ERTL (discontinued)
- Wooden Railway (2000, 2003 and battery powered; reintroduced 2014 "limited release"; discontinued)
- Take Along (normal and metallic; discontinued)
- Motor Road and Rail (discontinued)
- TrackMaster (discontinued)
- My First Thomas (interactive; discontinued)
- Thomas Engine Collection Series (discontinued)
- Mini Die Cast Collection (discontinued)
- Thomas Town (discontinued)
- Nakayoshi (discontinued)
- Woody Capsule Series (discontinued)
- Capsule Plarail (normal and metallic; discontinued)
- Pocket Fantasy (discontinued)
- Brio (discontinued)
- Trading Cards (discontinued)
- Bandai (discontinued)