Dench was born in Heworth, North Riding of Yorkshire. Her mother, Eleanora Olive (nee Jones), was born in Dublin, Ireland. Her father, Reginald Arthur Dench, a doctor, was born in Dorset, England, and later moved to Dublin, where he was brought up. He met Dench's mother while he was studying medicine at Trinity College, Dublin.

On 5 February 1971, Dench married British actor Michael Williams. They had their only child, Tara Cressida Frances Williams, an actress known professionally as Finty Williams, on 24 September 1972. Dench and her husband starred together in several stage productions and on the Bob Larbey British television sitcom, A Fine Romance (1981-84). Michael Williams died from lung cancer in 2001, aged 65. They have one grandchild, Finty's son Sam Williams (born in 1997). Dench has been in a relationship with conservationist David Mills since 2010. During a 2014 interview with The Times magazine, she discussed how she never expected to find love again after her husband's death, "I wasn't even prepared to be ready for it. It was very, very gradual and grown up ... It's just wonderful." In early 2012, Dench discussed her macular degeneration, with one eye "dry" and the other "wet", for which she has been treated with injections into the eye. She said that she needs someone to read scripts to her. She also underwent knee surgery in 2013, but stated that she recovered from the procedure well and "It's not an issue for me." Dench has been critical of prejudice in the movie industry against older actresses. She stated in 2014, "I'm tired of being told I'm too old to try something. I should be able to decide for myself if I can't do things and not have someone tell me I'll forget my lines or I'll trip and fall on the set"; and "Age is a number. It's something imposed on you ... It drives me absolutely spare when people say, 'Are you going to retire? Isn't it time you put your feet up?' Or tell me [my] age." In 2013, she spoke about her personal religious faith. Dench, a Quaker, said "I think it informs everything I do ... I couldn't be without it".

Are they still married?
she never expected to find love again after her husband's death,