The tournament was originally the championship of the , and was called the Western Open. In 1934 the Western Chess Association became the and the tournament became the American Chess Federation congress. In 1939, that organization merged into the United States Chess Federation (USCF) and the tournament became the U.S. Open.
In early years the tournament was usually small, and most years play was conducted as round robin. In some years it had to be divided into preliminary and final sections.
It grew larger starting in 1934, necessitating use of different formats. In 1946 the Swiss System was used for preliminary rounds, and in 1947 and subsequent years the tournament was held as a single section paired by the Swiss System.
For many years, the tournament had 12 or 13 rounds and lasted two weeks. After experimentation with various less-demanding formats, in recent years it has usually been nine rounds; the 2015 tournament was nine rounds in nine days.
Tournament participation grew through the 1950s and 1960s. Milwaukee 1953 had 181 entrants, setting a new record for the tournament. Cleveland 1957 had 184 players, and San Francisco 1961 set another attendance record with 198 players. The 1963 Open at Chicago had 266 entries, making it the largest chess tournament held in the United States to that time. The tourney was slightly smaller at Boston in 1964, with a field of 229.
The 1983 Open at Pasadena was the largest ever, at 836 official entries; it also featured the participation of Viktor Korchnoi, who had played in the last two World Championship matches.
In the 2000s, the fields were over 400 to 500 entries. The tournament began in some editions to decline both in attendance and importance, and often many winners are involved in a tie for first, especially since the mid 1990s.
The cash prizes awarded were large for their time and added to the tournament's popularity. In 1962, the entry fee was $20, with a first prize of $1,000, second prize $500, third $300, fourth $200, fifth $100, sixth through tenth $50 and eleventh through fifteenth $25. The Women's Open Champion won $200, and the women's runner-up $100. Additional cash prizes were awarded to the top women, the top junior, and for the best scores in the Expert, A, B, and C classes. The 2016 guaranteed prize fund was $40,000, with $8,000 for first place.
