Ray Kirton was diagnosed with Alzheimer's seven years ago aged 52.
His daughter, Mariel, from Leeds, has posted regularly since January 2015 to show "you can lead a happy life with the disease".
Ms Kirton, 21, said she also wanted to "tackle the stigma surrounding the brain disease".
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Her Instagram account now has more than 1,100 followers.
Ms Kirton was 14 when her father was diagnosed with the disease, having been misdiagnosed with depression.
"At 52, with a mind that still worked almost perfectly, dad was told that slowly he would lose all his memories, abilities and sense," she said.
Alarm bells rang when her father, a usually meticulous and hard-working medical sales manager, was put through disciplinary procedures for carelessness at work. His wife knew it was out of character.
Now 58, he can no longer drive, hold a conversation or remember the names of people closest to him.
Ms Kirton says her father's personality still shines through and the posts capture his daily activities and humour, love of music, precious moments with relatives and interaction with TV personalities.
"We are so lucky that he is still, for the most part, the happy and loving person he always has been," Ms Kirton said.
"Unfortunately his temperament is changing, with a bit less patience and a bit more frustration, and we know this will only get worse."
Ms Kirton ran the Leeds Half Marathon in May for Alzheimer's Research UK.
Alzheimer's Research said a rare type of the disease affects people from their 40s, with only around 4% of sufferers under 65.
Tim Parry of the charity said: "Mariel's story is inspirational. Tackling the stigma surrounding dementia is a challenge we face every day."
"Her heart-warming Instagram posts not only raise awareness of the disease but also give a message of hope."
Ms Kirton said: "Although parts are going, they are still the person you once loved, so please make the effort to be there for people living with Alzheimer's and their superhero carers."
The daughter of a man with early-onset Alzheimer's has documented his "precious moments" and daily struggles using photos on Instagram.