The club announced last week that the 27-year-old had tragically passed away.
Cusack was the first player to reach 100 appearances for the club's women's team, and players and fans paid tribute to her before their game against Newcastle on Sunday, which they lost 8-0.
Per BBC Sport, Derbyshire Police have now confirmed that they were called to an address around 18:35 BST on Wednesday, and Cusack was pronounced dead at the scene.
A file will now be prepared for the coroner, but there is no assumption of suspicious circumstances.
Before the Blades played Newcastle, there was a minute's silence, while members of her family laid a wreath in the centre circle. Fans also applauded in the eighth minute, marking her squad number.
England's Lionesses and the Scotland women's team both paid tribute to Cusack by wearing black armbands during their Nations League encounter.
Cusack played for the Blades and also worked in the club's marketing department during her career.