The name Kelsie is a modern variant of the Scottish name Kelsey, which itself is derived from the Old English words "ceol" meaning ship and "ey" meaning island. This suggests that the name originated in coastal regions of Scotland where seafaring was a way of life.

The earliest recorded spelling of the name was Kelsey, which dates back to the Domesday Book of 1086 AD, a survey of landowners in England commissioned by William the Conqueror. In these early records, the name referred to a location in Lincolnshire, England called "Cauenay" which later became known as Kelsey.

One of the earliest known bearers of the name was Kelsey Bardolf, an English noblewoman who lived in the 12th century. She was the wife of William Bardolf, Lord of Wormegay, and their family held lands in Norfolk and Suffolk.

Another notable historical figure with the name was Kelsey Grammer, an American actor and producer best known for his role as Dr. Frasier Crane on the TV series Frasier. He was born in 1955 and has won numerous awards throughout his career.

In the 16th century, there was a Kelsey Rayner who served as a Member of Parliament for Exeter in 1553 during the reign of Queen Mary I of England.

Moving into the 20th century, Kelsey Hibbert was a Canadian professional ice hockey player who played for the Toronto St. Patricks and Hamilton Tigers in the National Hockey League from 1924 to 1927.

While the name Kelsie is a more recent spelling variation, it shares the same rich historical roots as the traditional Scottish name Kelsey, tracing back to the coastal regions of Scotland and early English settlements.