This may be well known to those on this site, but I thought I'd provide a list of Third System coastal defense forts. These were virtually all used during the Civil War, either as mustering points, training sites, POW installations, or actually used in battle. There were 42 new-construction forts and several appurtenant structures that made up the defensive works. The Army identified them from northeast to southwest, then up the Pacific Coast. I'll use the same order.
Fort Knox, Bucksport, ME: Fort
Fort Popham, Popham Beach, ME: Fort
Fort Gorges, Portland, ME: Fort
Fort Scammel, Portland, ME: Fort
Fort Preble, Portland, ME: Fort
Fort McClary, Kittery, ME: Fort
Fort Constitution, Portsmouth, NH: Fort
Fort Warren, Boston, MA: Fort
Fort Winthrop, Boston, MA: Tower and Batteries
Fort Independence, Boston, MA: Fort
Fort at Clarks Point (Taber), New Bedford, MA: Fort
Fort Adams, Newport, RI: Fort and Redoubt
Fort Trumbull, New London, CT: Fort
Fort Schuyler, New York, NY: Fort
Fort Totten, New York, NY: Fort
Fort Tompkins, New York, NY: Fort
Fort Richmond (Battery Weed), New York, NY: Fort
Fort Hamilton, New York, NY: Fort and Redoubt
Fort at Sandy Hook (Hancock), Sandy Hook, NJ: Fort
Fort Delaware, Pea Patch Island, DE: Fort
Fort Carroll, Baltimore, MD: Fort
Fort Monroe, Hampton, VA: Fort
Fort Calhoun (Wool), Hampton, VA: Fort
Fort Macon, Atlantic Beach, NC: Fort
Fort Caswell, Oak Island, NC: Fort
Fort Sumter, Charleston, SC: Fort
Fort Johnson Tower, Charleston, SC: Tower
Fort Pulaski, Tybee Island, GA: Fort
Fort Clinch, Fernandina Beach, FL: Fort
Fort Taylor, Key West, FL: Fort
Fort Jefferson, Dry Tortugas, FL: Fort
Fort Pickens, Pensacola, FL: Fort
Fort Barrancas, Pensacola, FL: Fort
Advanced Redoubt, Pensacola, FL: Fort
Fort McRee, Pensacola, FL: Fort
Fort Morgan, Mobile, AL: Fort
Fort Gaines, Mobile, AL: Fort
Fort Massachusetts, Ship Island, MS: Fort
Fort Pike, New Orleans, LA: Fort
Fort Wood (Macomb), New Orleans, LA: Fort
Battery Bienvenue, New Orleans, LA: Battery
Tower Dupre, New Orleans, LA: Tower
Proctor's Tower (Fort Beauregard), New Orleans, LA: Tower
Fort Jackson, New Orleans, LA: Fort
Fort Livingston, New Orleans, LA: Fort
Fort Point, San Francisco, CA: Fort
Ten Gun Battery, San Francisco, CA: Battery
Fort Alcatraz, San Francisco, CA: Fort
Black Point Battery, San Francisco, CA: Battery
Lime Point Battery, San Francisco, CA: Battery
Battery Stevens, Columbia River, OR: Battery
Of course there were many older forts and towers that were upgraded to serve as part of the system. This list includes only new construction. A classic example of an older fort that was upgraded as part of the system was Fort Moultrie in Charleston, SC.
Fort Knox, Bucksport, ME: Fort
Fort Popham, Popham Beach, ME: Fort
Fort Gorges, Portland, ME: Fort
Fort Scammel, Portland, ME: Fort
Fort Preble, Portland, ME: Fort
Fort McClary, Kittery, ME: Fort
Fort Constitution, Portsmouth, NH: Fort
Fort Warren, Boston, MA: Fort
Fort Winthrop, Boston, MA: Tower and Batteries
Fort Independence, Boston, MA: Fort
Fort at Clarks Point (Taber), New Bedford, MA: Fort
Fort Adams, Newport, RI: Fort and Redoubt
Fort Trumbull, New London, CT: Fort
Fort Schuyler, New York, NY: Fort
Fort Totten, New York, NY: Fort
Fort Tompkins, New York, NY: Fort
Fort Richmond (Battery Weed), New York, NY: Fort
Fort Hamilton, New York, NY: Fort and Redoubt
Fort at Sandy Hook (Hancock), Sandy Hook, NJ: Fort
Fort Delaware, Pea Patch Island, DE: Fort
Fort Carroll, Baltimore, MD: Fort
Fort Monroe, Hampton, VA: Fort
Fort Calhoun (Wool), Hampton, VA: Fort
Fort Macon, Atlantic Beach, NC: Fort
Fort Caswell, Oak Island, NC: Fort
Fort Sumter, Charleston, SC: Fort
Fort Johnson Tower, Charleston, SC: Tower
Fort Pulaski, Tybee Island, GA: Fort
Fort Clinch, Fernandina Beach, FL: Fort
Fort Taylor, Key West, FL: Fort
Fort Jefferson, Dry Tortugas, FL: Fort
Fort Pickens, Pensacola, FL: Fort
Fort Barrancas, Pensacola, FL: Fort
Advanced Redoubt, Pensacola, FL: Fort
Fort McRee, Pensacola, FL: Fort
Fort Morgan, Mobile, AL: Fort
Fort Gaines, Mobile, AL: Fort
Fort Massachusetts, Ship Island, MS: Fort
Fort Pike, New Orleans, LA: Fort
Fort Wood (Macomb), New Orleans, LA: Fort
Battery Bienvenue, New Orleans, LA: Battery
Tower Dupre, New Orleans, LA: Tower
Proctor's Tower (Fort Beauregard), New Orleans, LA: Tower
Fort Jackson, New Orleans, LA: Fort
Fort Livingston, New Orleans, LA: Fort
Fort Point, San Francisco, CA: Fort
Ten Gun Battery, San Francisco, CA: Battery
Fort Alcatraz, San Francisco, CA: Fort
Black Point Battery, San Francisco, CA: Battery
Lime Point Battery, San Francisco, CA: Battery
Battery Stevens, Columbia River, OR: Battery
Of course there were many older forts and towers that were upgraded to serve as part of the system. This list includes only new construction. A classic example of an older fort that was upgraded as part of the system was Fort Moultrie in Charleston, SC.