Fairfield, the county seat of Freestone County, is at the junction of Interstate Highway 45, U.S. highways 75 and 84, and Farm roads 27, 488, and 1580, in the center of the county. The site was originally called Mound Prairie, but the name was changed to Fairfield when the location was chosen for the county seat in 1850. The original townsite, 100 acres of the Redin Gainer league, was donated by David Hall Love. In 1851–52, 128 lots were auctioned off for prices ranging from six dollars to $101. Rich farmland, vast amounts of timber, clear springs, and proximity to the Trinity River for transportation attracted settlers from the eastern states. Fairfield acquired a post office in 1851 and by September 1852 had three dry-goods stores, two hotels, a grocery, and a jail. A Fairfield Masonic lodge chartered in 1853 was still active in 1989. The first of four courthouses, a small wooden building described as "no better than a pigsty," was built about 1852. New courthouses were built—in 1854–56, at a cost of $8,330; in 1891–92, at a cost of $22,120; and in 1919–21, at a cost of $125,000. In 1891 and 1918 the need for a new courthouse led to county-seat elections in which Fairfield defeated Wortham and Teague, respectively.
A weekly newspaper, the Texas Pioneer, was established at Fairfield in 1857. Subsequent newspapers included the Ledger (1869–72) and the Recorder, first published in 1876 and still in existence in the 1990s. In the fall of 1854 a school for girls opened in a new two-story building, the upper floor of which was used as a Masonic hall. A school for boys seems to have opened in a different building in 1856. The first session at Fairfield Female College was held in 1859 under the direction of Henry Lee Graves. The school offered preparatory and college curriculum and enrolled over 100 students in its first year. The college remained open during the Civil War, when its enrollment actually increased because of an influx of Southern refugees. Freestone County was one of four Texas counties in which martial law was declared during Reconstruction. On October 9, 1871, Governor Edmund J. Davis imposed martial law in the county in response to reports of coercion and fraudulent voting in Fairfield during the election of October 3–6. Martial law was lifted a month later, on November 10. By 1884 Fairfield reported a population of 500. The community had two hotels, four general stores, and five groceries and served as a shipping point for cotton and hides. By 1892 the town had a bank and Baptist, Methodist, and Cumberland Presbyterian churches.
The community experienced a series of reverses around 1900. A meningitis outbreak killed thirty-two people in 1890, a tornado heavily damaged the central area of town in 1902, the boll weevil scourge destroyed the cotton crop in 1903, and fire ravaged part of the business district in 1911. Nevertheless, the population advanced steadily, to 629 by 1904, 1,047 by 1940, 2,074 by 1970, and 4,093 by 1988. Fairfield never acquired a railroad. The Trinity and Brazos Valley bypassed the town by ten miles when it built its track through Freestone County in 1906–07. Although the lack of a railroad did not cause Fairfield to decline, it did deprive it of a strong economic stimulus. The town obtained water and sewer lines in 1933 and a public library in 1954.
From 1890 to 1931 and again in 1933, Fairfield was the site of an annual reunion of Confederate veterans, who held their three-day gathering on land donated by William Lewis Moody and his brother Leroy. In 1951 the town held its centennial celebration on the old reunion campground. The success of the centennial led the townspeople to begin holding an annual rodeo-homecoming festival, which evolved into the county fair held each November. Other annual events include the Queen of the Trinity Star Pilgrimage in the spring, the National Coon Hunters Association meeting in the fall, and an arts and crafts fair in November. Local attractions and recreation facilities include the Freestone County Historical Museum (in Fairfield), and Fairfield Lake State Park (completed in 1972). In 1989 industries in Fairfield included TU Electric, Dow Chemical, TXO Production Corporation, and Texas Utilities Mining Company. Major sources of income were oil, gas, and coal mining, as well as agribusiness. Noted Fairfield residents have included L. D. Bradley, a Texas legislator, district judge, and commander of Company B, Second Battalion, Waul's Legion; John Gregg; and William L. Moody. The population was 3,234 in 1990 and 3,094 in 2000.