Fort Yamhill, on the Grand Ronde Indian Reservation, was established in March 1856. A detachment of troops, dragoons -mounted infantry- were assigned to the fort to keep the Indians on the reservations and to keep the white people off the reservation and away from the Indians. Too often, the tribes were being attacked by the white militant settlers, and too often the tribal people were influenced by liquor, and other inducements, to sell all they had to whites. The Indian office and the military set about to remove the tribes from direct contact with the whites, and to establish a series of forts to enforce order for both populations. These forts were Fort Umpqua, situated to manage travel and relations south of the Coast reservation at the Umpqua River, and to help gather up the remaining tribal peoples to the Coast Reservation; Fort Hoskins, to control travel from the Siletz Valley and the central section of the Coast Reservation into the Willamette Valley; and Fort Yamhill, to control persons traveling to and from the Reservation and the upper Willamette Valley. The troops at the fort maintained order at the reservations, using the forts for jails for violent or intoxicated Indians, and are sent on assignments to collect and return Indians who have escaped the reservations and are making a ruckus wherever they gather in or on the edge of the settler towns. There is never an uprising at the reservations, so the forts are never used to their full measure, to protect the troops from an Indian attack.
It was illegal to sell liquor to Indians, that this was a major trade that the Indian Superintendent and the military was to control, as well, it was illegal for the tribal people to leave the reservation, so Fort Yamhill was situated on a hill -now Fort Hill- alongside the Salmon River Wagon Road, and overlooking the pass into the Yamhill Valley. Lieutenant Philip Sheridan was assigned to the fort from nearly its creation and helped plan the siting of both forts Yamhill and Hoskins. Lt. Sheridan was in charge of the fort for a short time, June-August 1861, until he is called into service in the Civil War where he distinguishes himself as a hero of the war for the Union. The fort is established in March of 1856 and remained occupied until March 1866. Captain L. S. Scott of the 4th California Volunteers in 1864 is assigned to Fort Yamhill with his Company D, and is the last commander of the fort before it is decommissioned (Special order 121, September 23, 1864). The army would own the property for some time and would pass oversight to the Indian Office to be used for reservation lands.
Likely the first map to situate Fort Yamhill is the Hazen map of 1856.

The Smith Map of 1856 plans more directly the roads and features of the reservation. It would be interesting to understand more completely the relationship between the two maps from 1856.

The Smith Map is also in the Fort Hoskins Microfilm Records (Available at the Oregon State Archives.)

C. Gardner draws another map of Fort Yamhill in 1858 with updated layout, with proposed additional buildings. Note the additional roads, besides the Salmon River Wagon road, on left.

Finally the Fort Yamhill Plan of 1864.

When the fort is decommissioned the buildings are likely taken apart and the boards used to build other reservation buildings. The Fort itself is moved to Old Grand Ronde and is used as a police station jail until just before 1900.

In 1911 the fort is sold and moved to Dayton and situated in the central park square of the town. Fort Yamhill today remains in a rebuilt and restored condition in Dayton, Oregon.

The Officers quarters, remain at Fort Hill. The building has been investigated (History Detectives) and determined to have been the original building which was later added onto. Today, the Fort Yamhill State Heritage Park has undergone numerous archaeological investigations by David Brauner (OSU) and is slated to be developed into a replica fort in the future with rebuilt facilities for tourism. Oregon State Parks now works with the Grand Ronde tribe on interpretation and programming, because the tribe owns much of the acreage around the park, which has become the tribe’s Cultural use area, including Pow wow grounds, and Chachalu Plankhouse.

References
Fort Yamhill Heritage Area State Park Master Interpretive plan
Dayton Interpretive sign, plan
Microfilm records of the U.S. Adjutant General, Film 2, Fort Hoskins, Oregon State Archives, Salem