Magruder was a dedicated worker in the resistance against the British government, as were many in the Magruder family. Most were farmers, merchants and mechanics who had promised their fortunes in the quest for independence and for the cause of liberty.
Zadok Magruder was born in Prince George's County, Maryland, in 1729. The Magruder family was originally from Scotland. Zadok Magruder and his brother Nathan Magruder were the third generation of Magruders who were born in the Thirteen Colonies. Zadok and Nathan Magruder were the sons of John and Susanna Magruder, and the grandsons of Samuel and Sarah Magruder. Zadok Marguder's great-grandfather, Alexander Magruder, was deported from Perthshire, Scotland, in 1652, where he was an indentured servant pursuing the Scottish Rebellion. Alexander Magruder arrived in Prince George's County in 1652.
In 1745, Zadok Magruder inherited six hundred acres of land near Norbeck from his father, John Magruder. Zadok Magruder built a house five years later in 1750 in Redland, a community which had a population of about fifty at the time. Four years later in 1754, he married Rachel Pottinger Bowie and they had eleven children, eight girls and three boys, one of whom, named Zadok, later became a doctor. Magruder later lived in an area known as Mount Pleasant, where there were many large family farms. This area belonged to Magruder and he is said to have built a house, named Mount Pleasant, in that spot in about 1807. After Magruder died, the region belonged to his son and heir, Robert Pottinger Magruder.
Zadok Magruder and his brother Nathan Magruder were members of the General Committee to Annapolis in 1774 (as local representatives). The General Committee to Annapolis functioned as the state or colony level of government for Maryland. Zadok and Nathan became members of a committee charged with carrying out the decision of the American Continental Congress on the topic of the British Tea Act. Zadok Magruder became a member of the Maryland Committee of Correspondence. When Zadok was in command of the "Home Defense Battalion of Lower Frederick County", which was part of the Maryland militia, he attained the rank of colonel. Zadok was later appointed, with his brother Nathan, as a commissioner to organize and establish the government of Montgomery County when it became a separate county from Fredrick County in 1776.
A high school named after Colonel Zadok Magruder was built in Derwood (Montgomery County), Maryland. Colonel Zadok A. Magruder High School is near the site of "The Ridge", the Zadok Magruder family home in Redland.