Grundy County's recorded history began in the early 1800's. The first settlers in Grundy county were General W.P. Thompson and his family, who arrived in 1833. General Thompson's home still stands today, located in Crowder State Park, along the Thompson River.
About a year after Thompson settled, Levi Moore and his family arrived, and the area soon after became known as "Moore's Settlement". In 1838 the first store opened in what was then called Lomax.
Grundy County was organized in 1841 with set boundaries. The county was named for Felix Grundy, Tennessee senator and United States attorney general under President Jackson. In 1857, the county seat of Grundy County - Trenton, was born. The first court in Grundy County was held in a log house in Trenton (known then as Lomax Store).
One of the county's main businesses from 1873 to 1943 was mining. There were three different coal mines in the area, along with a major railroad, which helped the mining industry here to thrive.
The current courthouse was built in 1903, and is still in excellent condition. Grundy County is classified as a third class county with a township form of government. The current assessed valuation is over $131 million for a population of around 10,197 (according to the 2010 census). Grundy County encompasses over 437 square miles, and has an agricultural based economy.