William Neilson Gemmill (14 June 1900 – 18 September 1987) was a Welsh cricketer.
Gemmill was a right-handed batsman who bowled right-arm medium-fast.
He was born in Thio on the French Pacific island of New Caledonia.
Gemmill made his debut for Glamorgan when the Welsh county was still a Minor county, making his first appearance for the county against Cheshire in the 1920 Minor Counties Championship.
He played a further match for the county that season, against Devon.
After the 1920 season, Glamorgan were given first-class status for the 1921 season.
It was in this season that Gemmill made his first-class debut in the County Championship against Leicestershire.
He played first-class cricket for Glamorgan from 1921 to 1926, making 47 first-class appearances.
In his 47 first-class matches for Glamorgan, he scored 1,169 runs at an average of 13.59, with a high score of 77.
This score, one of four fifties he scored for Glamorgan, came against Sussex in the 1922 County Championship.
He also made a single first-class appearance for Wales in 1923 against Scotland.
In this match, he scored 74 runs in the Welsh first-innings, before being dismissed by John Fergusson, with Wales winning by an innings and 111 runs.He died in Canterbury, Kent, England on 18 September 1987.