Patrick Rogers, 26, died in the two-car collision near Cookstown on Monday.
His mother-in-law Mary Duffy, 52, was also killed while his wife Shannon and four children, Alannah, Eimear, Dylan and Eli, were injured.
The driver of the other vehicle, named locally as Jennifer Acheson, who was in her 80s, also died in the crash, which occurred shortly before 3.30pm on the Dungannon Road outside Cookstown.
Funeral mass was held for Mr Rogers at St Joseph and St Malachy’s church in nearby Drummullan on Friday.
Ms Rogers and the children could not attend the service. Mourners heard she was watching on a webcam.
During the service, a letter she wrote to her husband after his death was read to the church.
“To my dear husband, you were my everything, my best friend, my soulmate,” she wrote.
“You had the best brown eyes, gentle hands and the kindest heart.
“You were the best dad, always cracking jokes, the biggest entertainer, you were the tickle master, so young at heart.
“You were also the most competitive – you never let us win on the Xbox or Mario Kart.
“I will love you always and I will be looking up at you when I need help and guidance.”
After the funeral, Mr Rogers’ remains were taken to the adjacent cemetery for burial.
Mourners formed a guard of honour outside as his coffin was carried from the church.
Funeral mass for Ms Duffy will be held at St Patrick’s Church in Dungannon on Saturday.
The funeral for Ms Acheson will also be held on Saturday morning, at Desertcreat Parish Church.