In 1887, the Linn County Pioneer Association was formed to plan a reunion for homesteaders of Linn County. Originally called the Linn County Pioneers' Reunion, the name was changed to Linn County Pioneer Picnic after the original pioneers had died. The Pioneer Picnic has never been canceled, although it was nearly rained out a few times, making it the oldest continuous annual pioneer celebration in Oregon. 

The original Pioneers’ Reunion board members were George F. Colbert, Robert Glass, Wilson B. Glass, James W. Gay, Dr. G.W. Gray, William McCaw, J.H. Scott, James Norval Rice, and Rev. Robert Robe. The Linn County Pioneer Association continues to manage the picnic, which is funded by local businesses, vendor fees, and ticket sales for the games and rides. 

The picnic hosts several activities, including exhibits, entertainment, and family and high school reunions. The three-day event begins on a Friday in June with a Kiddie Parade and the crowning of the Linn County Pioneer Picnic Queen. On Saturday morning, the streets of Brownsville are filled with people waiting for the Grand Parade, which features the grand marshal and the queen and her court. In the early years of the picnic, pioneers marched in a procession to a small wooded park in Brownsville; today, spectators follow the parade to the same park, now called Pioneer Park. Entrance to the event has always been free.

Picnic participants display their talents in a quilt show, flower show, and art display. Athletic events include a horseshoe tournament, basketball and baseball tournaments, horse-riding contests, a fun run/walk, and a logging skills competition. Family activities include a penny scramble, three-legged races, and an egg-tossing contest. Horse and logging activities and the Sunday morning nondenominational church service date to the early years of the picnic.

People gather at a pavilion that the Association built many years ago to visit, attend the fireman’s breakfast (which raises money for the Brownsville Fourth of July fireworks show), and eat lunch and dinner. The Brownsville Recreation Center provides the food as a fundraiser. 

Pioneer Picnic events have varied over time based on interest, cost, risks, and environmental concerns. A carnival, which was a popular part of the event at the turn of the twentieth century, has been replaced by an inflatable bounce apparatus, carnival games sponsored by local organizations, and food and other vendors. For many years, the governor, senators, political candidates, and local celebrities took the stage to speak. The programs today tend to be more active, with pie-eating contests, talent shows, and dance recitals.