Eddy was born Mary Morse Baker in a farmhouse in Bow, New Hampshire, to farmer Mark Baker (d. 1865) and his wife Abigail Barnard Baker, née Ambrose (d. 1849).
Eddy was the youngest of the Bakers' six children: boys Samuel Dow (1808), Albert (1810), and George Sullivan (1812), followed by girls Abigail Barnard (1816), Martha Smith (1819), and Mary Morse (1821).

Mark Baker was a strongly religious man from a Protestant Congregationalist background, a firm believer in the final judgment and eternal damnation, according to Eddy.
McClure's magazine published a series of articles in 1907 that were highly critical of Eddy, stating that Baker's home library had consisted of the Bible.
Eddy responded that this was untrue and that her father had been an avid reader.
According to Eddy, her father had been a justice of the peace at one point and a chaplain of the New Hampshire State Militia.
He developed a reputation locally for being disputatious; one neighbor described him as "[a] tiger for a temper and always in a row."
McClure's described him as a supporter of slavery and alleged that he had been pleased to hear about Abraham Lincoln's death.
Eddy responded that Baker had been a "strong believer in States' rights, but slavery he regarded as a great sin."

The Baker children inherited their father's temper, according to McClure's; they also inherited his good looks, and Eddy became known as the village beauty.
Life was nevertheless spartan and repetitive.
Every day began with lengthy prayer and continued with hard work.
The only rest day was the Sabbath.
Eddy was born Mary Morse Baker in a farmhouse in Bow, New Hampshire, to farmer Mark Baker (d. 1865) and his wife Abigail Barnard Baker, née Ambrose (d. 1849). Eddy was the youngest of the Bakers' six children: boys Samuel Dow (1808), Albert (1810), and George Sullivan (1812), followed by girls Abigail Barnard (1816), Martha Smith (1819), and Mary Morse (1821).
Mark Baker was a strongly religious man from a Protestant Congregationalist background, a firm believer in the final judgment and eternal damnation, according to Eddy. McClure's magazine published a series of articles in 1907 that were highly critical of Eddy, stating that Baker's home library had consisted of the Bible. Eddy responded that this was untrue and that her father had been an avid reader. According to Eddy, her father had been a justice of the peace at one point and a chaplain of the New Hampshire State Militia. He developed a reputation locally for being disputatious; one neighbor described him as "[a] tiger for a temper and always in a row." McClure's described him as a supporter of slavery and alleged that he had been pleased to hear about Abraham Lincoln's death. Eddy responded that Baker had been a "strong believer in States' rights, but slavery he regarded as a great sin."
The Baker children inherited their father's temper, according to McClure's; they also inherited his good looks, and Eddy became known as the village beauty. Life was nevertheless spartan and repetitive. Every day began with lengthy prayer and continued with hard work. The only rest day was the Sabbath.
Mary Baker Eddy