“The Republic of Gilead knows no bounds. Gilead is within you.”— Aunt Lydia to the Handmaids in the Red Center .
A map presented during an event for the season 2 finale revealed the full extent of the Republic of Gilead. It has largely taken control of most of what was the United States with the eastern, northeastern, and mid-western parts of the country being in Gilead hands (as evident with these particular areas being in a shade of blue on the map), but anti-Gilead/pro-US forces have retained control of the entire West Coast and the Gulf Coast including most of Texas and all of Florida. Rebel forces also control a large tract of territory along the Canadian border and northern Michigan along with an enclave in New England centering around Vermont, New Hampshire, and parts of Maine and New York state.
As shown in the map in the season two finale, it can be implied that the zones highlighted in blue are territories controlled exclusively by the Republic of Gilead. This falls in line with the limited details in the novel and the fact that most of the action in the novel took place on the East Coast and because Washington, D.C. was the first to "fall" given the attacks on Congress, the White House, and the Supreme Court.
Geographic Information from the Storyline
In the TV series, a scene from the Holly episode inside the MacKenzie household shows three maps along the wall. When searching for Commander MacKenzie's car keys, maps can be found behind June on the wall which show the opening, middle and later stages of the civil war between the US and Gilead. The end result being American forces largely being pushed off the Lower 48 states.
Offred mentions in her inner monologue in Episode 2 that "Guardians of the Faithful and American soldiers still fight with tanks in the remains of Chicago", confirming that the Second American Civil War is still ongoing.
In addition to this, the official United States government operating out of Anchorage has total control over Alaska and Hawaii. Their level of influence over the rebel-held areas of the former US, such as California and Texas, remains to be seen.
Areas euphemistically termed "the Colonies" exist, which have been ecologically contaminated - apparently due to a mixture of industrial pollution, chemical/radiological accidents, and chemical/possibly-nuclear warfare. The Colonies are located in what was once the American mid-west and south-west. Gilead condemned criminals and "Unwomen" to slave-labor on cleanup projects in the Colonies, which is essentially a death sentence.
The states that make up the Republic of Gilead in complete occupation are: Minnesota, Wisconsin, Illinois, Michigan, Indiana, Ohio, Tennessee, Kentucky, West Virginia, Virginia, North Carolina, Maryland, Pennsylvania, Delaware, New Jersey, New York, Connecticut, Rhode Island, Maine, New Hampshire, and Massachusetts.
Regions in the West and Midwest indicated in yellow in the map props from the show's production are referred to as colonies districts; these regions in the West and Midwest may have been destroyed as a result of the civil war following the takeover. Within these regions are two large sites in Arizona and Missouri that are marked as radioactive, presumably the sites of The Colonies where unwomen are sent to work in. These sites and two in rebel-occupied regions of California (one south of San Francisco/Bay area and the other spanning Los Angeles, Orange, and San Diego counties) correspond to one or more nuclear reactors according to a map from the US Nuclear Regulatory Commission. This appears to hint at the idea that one or more of these reactors were compromised in some way following the rise of Gilead.
Zones in the dark red and pink, located in both the West, Midwest, and South, are sites of active war between the military forces of the United States of America (along with rebel groups and unorganized citizen militia units loyal to the United States) and the Guardians of the Faith--the army of the Republic of Gilead. In addition to the mentioned rebel areas, there is a large American rebel stronghold located in New England with this stronghold centered in Vermont and parts of New Hampshire, Maine, and New York state. An opposition radio station (Radio Free America) airs in that region but broadcasted from Somewhere in Canada.
The number of states in which the former United States of America was divided into has also been reduced in favor of larger districts and wider boundaries.