Milton County, Georgia is an extinct county. It was created on December 18, 1857 from parts of northeastern Cobb, southeastern Cherokee, and southwestern Forsyth counties. It was created in order to have a more accessible county seat. Milton County was Georgia's 121st county.

The original boundaries were defined by an act of the General Assembly. (see: Ga. Laws 1857, p. 36).

Milton County was known for it's rich farming land and abundant, rich and high-quality cotton crops. It's residents were known for experimenting with their crops to develop finer quality and higher yields of cotton.

Alpharetta was the county seat until the end of 1931, when Milton was merged with Fulton County. The city of Alpharetta was incorporated and designated the county seat on December 11, 1858. It evolved from New Prospect Campground which consisted of Methodist settlements of tents and other temporary housing. The name 'Alpharetta' is Greek for 'First Town'.

Milton County was merged with Fulton County January 1, 1932. Because the economy of the county was primarily dependent on cotton it was vulnerable to weather. With the infestations of the boil weevil in the 1910s and 1920s and then the Depression of the 1930s, the county became destitute. Milton County was merged with Fulton County in order for the county residents to benefit from the more stable economy of Fulton County. At the same time the town of Roswell (Cobb County) and Campbell County were also ceded to Fulton County. This gave Fulton it's 70-mile long irregular shape along the Chattahoochee River. The cession of Roswell (including verything east of Willeo Creek) was necessary to make the new county contiguous.

Milton County was named for John Milton (circa 1740 - 1817), Georgia's first secretary of state (1777 - 1799), who was elected three times. He was a candidate for and received 2 electoral votes for President of the United Sates in 1789. A lieutenant colonel in the Revolutionary War, he is credited with saving and preserving the state's official records during the British occupation. During the American Revolution, Milton served in the First Georgia Regiment and later as aide-de-camp to Gen. Benjamin Lincoln and Col. Francis Marion. In late 1779 or early 1780, fearing British capture of the state's records, Milton had them transferred to Charleston, then to New Bern, North Carolina, and finally to Maryland. More about John Milton.

Some say Milton County was named for Homer V. Milton, a descendant of John Milton and a General in the War of 1812.

In recent years, some residents unhappy with the distribution of Fulton County's municipal services between urban Atlanta and their northern suburbs have sought to re-create Milton County, consisting of Roswell, Alpharetta, and Mountain Park. A bill before the Georgia General Assembly in 2005 proposes to include Sandy Springs as well, and rename the remainder of Fulton County as "Atlanta County". The state's constitution, however, now prohibits any more than 159 counties, the number it has had since the merger in 1932. Any change would require a constitutional amendment, supported by two-thirds of each house in the state legislature, and by over half of all voters statewide in a referendum.