1850 Atlas
| Name | What | Place | Pop | Other |
| Siam | PO | Leon Co, TX | ||
| Siasconset | V | Nantucket Co, MA | on Nantucket island, water by Atlantic ocean | |
| Sibila | PO | Washington parish, LA | ||
| Sibley | PO | Jackson Co, MO | ||
| Sibley's Mils | PO | Wilkinson Co, MS | ||
| Sicily | PO | Highland Co, OH | ||
| Sidney | PT | Kennebec Co, ME | 1,955 | water by Kennebec river |
| Sidney | PT | Delaware Co, NY | 1,807 | water by Oleout creek |
| Sidney | PO | Hunterdon Co, NJ | ||
| Sidney | PT, CH | Shelby Co, OH | 1,302 | seat of justice, water by west branch of Great Miami river |
| Sidney | PV | Marshall Co, IN | ||
| Sidney | PO | Fremont Co, IA | ||
| Sidney Centre | PO | Sidney twp, Delaware Co, NY | ||
| Sidney Plains | PV | Sidney twp, Delaware Co, NY | water by Susquehanna river | |
| Sidon | PO | Carroll Co, MS | ||
| Sidonsburgh | PO | York Co, PA | ||
| Siegel's Store | PO | Lincoln Co, NC | ||
| Sigourney | PV, CH | Keokuk Co, IA | 162 | seat of justice |
| Siloa | PO | Sullivan Co, IN | ||
| Siloam | PV | Smithfield twp, Madison Co, NY | ||
| Siloam | PV | Surry Co, NC | ||
| Silvan | T | Washtenaw Co, MI | 1,343 | |
| Silver Creek | PO | Hanover twp, Chautauque Co, NY | ||
| Silver Creek | PT | Greene Co, OH | 2,585 | |
| Silver Creek | PO | Cass Co, MI | water by Dowaglake river | |
| Silver Creek | PO | Madison Co, KY | ||
| Silver Creek | PO | Maury Co, TN | ||
| Silver Creek | PO | Stephenson Co, IL | ||
| Silver Glade | PO | Anderson dist, SC | ||
| Silver Hill | PO | Davidson Co, NC | ||
| Silver Lake | PT | Susquehanna Co, PA | 1,213 | water by Silver lake & Silver creek |
| Silver Lake | PO | Washtenaw Co, MI | ||
| Silver Lake | PO | Waushara Co, WI | ||
| Silver Run | PO | Talladega Co, AL | ||
| Silver Run | PO | Meigs Co, OH | ||
| Silver Spring | PT | Cumberland Co, PA | 2,308 | water by Conedogwinit creek |
| Silver Spring | PO | St Francis Co, MO | ||
| Silverton | PV | Barnwell dist, SC | water by Savannah river | |
| Silver Top | PO | Obion Co, TN | ||
| Silverville | PO | Lawrence Co, IN | ||
| Simmons | PO | Lawrence Co, OH | ||
| Simm's Port | PV | Avoyelles parish, LA | ||
| Simmonsville | PO | Giles Co, VA | ||
| Simonsville | PV | Windsor Co, VT | ||
| Simpson's | PO | Floyd Co, VA | ||
| Simpson's Mill | PO | Laurens dist, SC | ||
| Simpson's Store | PO | Washington Co, PA | ||
| Simpsonville | PO | Shelby Co, KY | water by Floyd's fork of Salt river | |
| Simpsonville | PO | Anne Arundell Co, MD | ||
| Simbury | PT | Hartford Co, CT | 2,737 | |
| Sina | PT | Clinton Co, MI | ||
| Sinclair's Bottom | PO | Smyth Co, VA | ||
| Sing Sing | PV | Mount Pleasant twp, Westchester Co, NY | water by Hudson river, site of state prison | |
| Sinking Creek | PO | Botetourt Co, VA | ||
| Sinking Creek | PO | Bedford Co, TN | ||
| Sinking Spring | PO | Berks Co, PA | ||
| Sinking Spring | PV | Brush Creek twp, Highland Co, OH | ||
| Sinking Spring | PO | Lawrence Co, IN | ||
| Sinking Valley Mills | PO | Blair Co, PA | ||
| Sinnamahoning | PO | Clinton Co, PA | ||
| Sipesville | PO | Somerset Co, PA | ||
| Sippican | PV | Rochester twp, Plymouth Co, MA | ||
| Sipsey Turnpike | PO | Tuscaloosa Co, AL | ||
| Sir John's Run | PO | Morgan Co, VA | ||
| Sissonville | PV | Kanawha Co, VA | water by Pocotalico river | |
| Sisterdale | PO | Comal Co, TX | ||
| Sistersville | PV | Tyler Co, VA | water by Ohio river | |
| Six Corners | PO | Richland Co, OH | ||
| Six Mile | PO | Jennings Co, IN | ||
| Six Mile | T | Madison Co, IL | ||
| Six Mile Falls | PO | Penobscot Co, ME | ||
| Six Mile Run | PO | Somerset Co, NJ | ||
| Six Mile Run | PO | Bedford Co, PA | ||
| Six Runs | PO | Sampson Co, NC | ||
| Skaneatelers | PT | Onondaga Co, NY | 4,081 | water by Skaneateles Lake outlet |
| Skeel's Cross Roads | PO | Mercer Co, OH | ||
| Skegg's Creek | PO | Barren Co, KY | ||
| Skeinah | PO | Union Co, GA | ||
| Skelton | T | Warrick Co, IN | 532 | |
| Skinner's Eddy | PO | Wyoming Co, PA | water by Susquehanna river | |
| Skinquarter | PO | Chesterfield Co, PA | ||
| Skippack | PT | Montgomery Co, PA | water by Shippack creek | |
| Skitt's Mountain | not listed | Hull Co, GA | ||
| Skowhegan | PT | Somerset Co, ME | 1,756 | water by Kennebec river at Skowhegan falls |
| Slabtown | PV | Anderson dist, SC | ||
| Slack | PO | Mason Co, KY | ||
| Slade | PO | Lee Co, GA | ||
| Sladesville | not listed | Hyde Co, NC | ||
| Slash Cottage | PO | Hanover Co, VA | ||
| Slate | PO | Bath Co, KY | ||
| Slate Creek | PO | Tazewell Co, VA | ||
| Slate Ford | PO | Northampton Co, PA | ||
| Slate Hill | PO | Minisink twp, Orange Co, NY | ||
| Slate Hill | PO | York Co, PA | ||
| Slate Lick | PO | Armstrong Co, PA | ||
| Slate Mills | PO | Rappahannock Co, VA | ||
| Slaterville | PV | Smithfield twp, Providence Co, RI | water by tributary of Pawtucket river | |
| Slaterville | PV | Caroline twp, Tompkins Co, NY | water by Six Mile creek | |
| Slatington | PO | Lehigh Co, PA | ||
| Sleepy Creek | PO | Wayne Co, NC | ||
| Sleepy Creek | PO | Edgefield dist, SC | ||
| Sleepy Creek Bridge | PO | Morgan Co, VA | ||
| Sligo | PO | De Kalb Co, AL | ||
| Sligo | PO | Henry Co, TN | ||
| Sligo | PO | Clinton Co, OH | ||
| Slippery Rock | PO | Butler Co, PA | water by Slippery Rock & Wolf creeks | |
| Slippery Rock | PT | Beaver Co, PA | ||
| Slippery Rock | PT | Mercer Co, PA | ||
| Sloansville | PV | Schoharie twp, Schoharie Co, NY | water by Vly creek | |
| Sloatsburgh | PO | Rockland Co, NY | ||
| Sloyersville | PO | Luzerne Co, PA | ||
| Smelser's Mills | PO | Rush Co, IN | ||
| Smeltzer's Grove | PO | Grant Co, WI | ||
| Smicksburgh | PO | Indiana Co, PA | ||