Thomaston, formerly known as Fort St. Georges, Fort Wharf, and Lincoln, is a town in Knox County, Maine, United States. The population was 2,739 at the 2020 census. Noted for its antique architecture, Thomaston is an old port popular with tourists. The town was named after Major General John Thomas.

As early as 1630, a trading post was established on the eastern bank of the St. George River, then considered the boundary between New England and New France. In 1704, Thomas LeFebvre from Quebec bought a large tract of land along the Weskeag River on which he built a gristmill, with a house on the shoreline at what is now South Thomaston. Originally called Koessanouskek (or Kouesanouskek) by the French, the area became known as Thomas' Town.

Between 1719 and 1720, the old trading post was remodeled into Fort St. George, a stockaded fort protected by two blockhouses. But Abenaki Indian tribes protested the encroachment of an English fort on their territory. Instigated by the French, they attacked the garrison twice during Dummer's War in 1722, then again in 1723 with a siege lasting 30 days. In response to this and other provocations, soldiers destroyed the Abenaki stronghold of Norridgewock in 1724.

During the French and Indian War, to avenge the fall of Louisbourg, on August 13, 1758, French officer Boishebert left Miramichi, New Brunswick with 400 soldiers for Fort St George in Thomaston. His detachment reached there on September 9 but was caught in an ambush and had to withdraw. This was Boishébert's last Acadian expedition. They then went on to raid Friendship, Maine, where people were killed and others taken prisoner. Hostilities of the French and Indian Wars ceased with the 1759 Fall of Quebec.

Mason Wheaton was the first permanent settler in 1763. Located at the heart of the Waldo Patent, Thomaston was incorporated from St. Georges Plantation on March 20, 1777. Many settlers arrived following the Revolutionary War in 1783. General Henry Knox built his Montpelier mansion at Thomaston in 1793–1794.

The town prospered in the early 19th century as a port and ship building center. Around 1840, two of seven recorded millionaires in the United States were Thomaston sea captains. Other industries included two gristmills, two sawmills and planing mills, three sail lofts, brickyards, cask manufacturing and a marble works. Lime had been manufactured here since 1734 in kilns. Thomaston is still home to Jeff's Marine, Inc. and Lyman Morse Boatbuilding, builders of custom power and sailing yachts. Located on St. George River, Lyman Morse Boatbuilding sits on the original site of the General Henry Knox Mansion, where wooden schooners have been built for over 200 years.

Rockland and South Thomaston were set off and incorporated in 1848. The Knox and Lincoln Railroad passed through the town, carrying freight and tourists.

In June 1875, Louis Wagner, the Smuttynose Axe Murderer, and John True Gordon, known as the Thorndike Slayer, were hanged on the gallows of the then-Maine State Prison in Thomaston. Louis Wagner's burial site was unknown until the book Return to Smuttynose Island: And Other Maine Axe Murders by Emeric Spooner was released in 2009. Spooner located Wagner's grave which can still be viewed in the Old Prison Cemetery.