My definition of non-combatant will be civilian.
According to the National Consortium for the Study of Terrorism and Responses to Terrorism around 33,000 people were killed by ISIS or ISIS affiliated troops between 2002-2015, but it doesn't specify if they were civilians.
According to the UN 6,878 civilians died in Iraq last year in violence mainly inflicted by ISIS. They keep a running tally every month which can be found here
By 2016 ISIS had killed roughly 1200 people mostly civilians outside of Iraq and Syria.
The Syrian Observatory for Human Rights estimated in 2013, that 46,266 civilians had died so far in the Syrian conflict.
UNHCR reported in 2015 there estimates of civilian casualties in the Syrian conflict but didn't specify who killed them
From 1 January 2014 through 31 October 2015, UNAMI/OHCHR recorded at least 55,047 civilian casualties as a result of the conflict, with 18,802 people killed and 36, 245 wounded
The Syrian Network For Human Rights released a report in March 2017, which claims that 206,923 civilians have died in the Syrian conflict of which only 3352 were killed by ISIS (The full report is available here). This is a strange number in some regards because Airwars estimates a minimum of 3,962 civilians killed by coalition (American and NATO allies) air-strikes. So it would seem the American forces had killed more civilians in Syria than ISIS have.
So the only two number I could find which specify civilians killed by ISIS seems to be 3352 + 1200 = 4552.
Disclaimer: These numbers are realistically likely to be unreliable as there is very little accurate data to suggest the exact numbers killed by each force in the Syrian Civil War.