The Reddit user Malxredleader put together this excellent map of the oldest building in each US state. Below is a table that outlines all their dates of construction. You can read the full discussion on reddit here.
List of Oldest Buildings in Each US State
| U.S. State/Territory | Building | Year Built | Century Built |
|---|---|---|---|
| Alabama | Joel Eddins House | 1808 | 19th |
| Alaska | Kodiak History Museum | 1810 | 19th |
| Arizona | Ancestral Puebloan Dwellings | c. 750 CE | 8th |
| Arkansas | Woodruff Print Shop | 1824 | 19th |
| California | Mission San Juan Capistrano | 1776 | 18th |
| Colorado | Ancestral Puebloan Dwellings | c. 750 CE | 8th |
| Connecticut | Henry Whitfield House | 1640 | 17th |
| Delaware | Ryves Holt House | 1665 | 17th |
| District of Columbia | Old Stone House | 1765 | 18th |
| Florida | Castillo de San Marcos | 1672 | 17th |
| Georgia | Ocmulgee Earth Lodge | 1015 | 11th |
| Hawaii | Malae Heiau | 1200 | 11th |
| Idaho | Cataldo Mission | 1853 | 19th |
| Illinois | Old Cahokia Courthouse | 1740 | 18th |
| Indiana | Grouseland | 1804 | 19th |
| Iowa | Louis Arriandeaux Log House | 1833 | 19th |
| Kansas | El Quartelejo Ruins | 1650 | 17th |
| Kentucky | Historic Locust Grove | 1790 | 18th |
| Louisiana | Old Ursuline Convent | 1748 | 18th |
| Maine | William Whipple House | 1660 | 17th |
| Maryland | Old Trinity Church | 1675 | 17th |
| Massachusetts | Fairbanks House | 1641 | 17th |
| Michigan | Officer’s Stone Quarters | 1780 | 18th |
| Minnesota | Fort Snelling Round Tower | 1820 | 19th |
| Mississippi | LaPointe-Krebs House | 1757 | 18th |
| Missouri | Louis Bolduc House | 1792 | 18th |
| Montana | Old Fort Benton Blockhouse | 1844 | 19th |
| Nebraska | Log Cabin | 1835 | 19th |
| Nevada | Old Las Vegas Mormon Fort | 1855 | 19th |
| New Hampshire | Strawbery Banke | 1600 | 17th |
| New Jersey | Mortonson-Van Leer Log Cabin | 1654 | 17th |
| New Mexico | Ancestral Puebloan Dwellings | c. 750 CE | 8th |
| New York | Gardiners Island Shed | 1639 | 17th |
| North Carolina | Lane House | 1718 | 18th |
| North Dakota | Kittson Trading Post | 1843 | 19th |
| Ohio | Rufus Putnam House | 1788 | 18th |
| Oklahoma | Fort Gibson Barracks | 1840 | 19th |
| Oregon | Molalla Log House | 1799 | 18th |
| Pennsylvania | Lower Swedish Cabin | 1650 | 17th |
| Puerto Rico | Cathedral of San Juan Bautista | 1521 | 16th |
| Rhode Island | White Horse Tavern | 1673 | 17th |
| South Carolina | Middleburg Plantation | 1694 | 17th |
| South Dakota | Fort Sisseton | 1864 | 19th |
| Tennessee | Christopher Taylor House | 1778 | 18th |
| Texas | Alamo Mission Long Barracks | 1724 | 18th |
| Utah | Ancestral Puebloan Dwellings | c. 750 CE | 8th |
| Vermont | William Henry House | 1769 | 18th |
| Virginia | Jamestown Church | 1647 | 17th |
| Washington | Fort Nisqually Granary | 1843 | 19th |
| West Virginia | Rehoboth Church | 1785 | 18th |
| Wisconsin | Tank Cottage | 1776 | 18th |
| Wyoming | Fort Laramie ‘Old Bedlam’ Building | 1849 | 19th |