The junior corps was a parade unit during its first two years. When the senior Dukes of Dubuque folded in 1964, Clarence Hagge, Dick Davis and Bob Buelow took over the Junior Dukes, changing the name to the Legionnaires in 1965. Initially attempting to recruit 13- to 15-year-old boys, the corps began admitting girls in the fall of 1965.

When the Parents and Booster Club was formed on November 16, 1966, the corps had 75 members, all under 17 years old. The first trophy ever won by the corps came that year, a second place in the Hazel Green, Wisconsin, parade. The Cadets were formed in the fall of 1967 as a feeder corps for the "A" corps. Sonia Hickson was its first director.

The Legionnaires were incorporated as a non-profit organization in 1968, when they fielded 83 members. 1968 was also the first full year of competition, over some 4000 miles of travel. The corps brought home twelve trophies, including the 1968 State American Legion Junior Color Guard Championship. The City of Dubuque proclaimed the Legionnaires their "Junior Ambassadors of Goodwill" and presented the corps with the official Dubuque City flag.

The name change to the Colt .45 became official in 1968 so that the corps could perform in shows other than Legion sponsored events. This was the first year the Colt .45 adopted its all-Western uniforms (because "they were the cheapest") and music. The corps competed in Class A with their first field drill, and won almost all of the 18 events they entered, including the Mid-American Circuit Championship and the Iowa VFW Junior Championship. The purchase of the corps’ first truck was the corps' first big investment.

In 1970, the corps first performed the "Colt .45 Stomp,“ believed to be the first non-standard meter arrangement in drum corps history. Written in 7/4, the concept was so radical that some judges ticked the corps down for being out of step on every other downbeat.

1971 saw the Colt .45’s first national competition and the first time it performed on artificial turf, at the VFW Nationals in Dallas. The corps took first place at the American Legion Color Guard Championships.

By 1973, the corps had moved up to a fifth-place finish in the New Orleans VFW Nationals, as well as first in the parade competition. A pro football halftime show at Soldier Field entertained 56,000 fans that fall.

In 1976 the corps dropped the “.45” from its name, citing the association with guns and beer. The Colts fielded about 105 members in 1976, and its color guard also began competing in Winter Guard.

The corps finished 26th at the DCI Championships in Denver in 1977, but due to the disqualification of another corps, were officially ranked 25th, the first time they cracked the top 25. That may have been partially due to the new riverboat gambler uniform designs, created by Drum Corps World publisher Steve Vickers.

1978 was a watershed year for the Colts. A disappointing 27th place finish and a large membership turnover led to a consolidation of a core family philosophy, and a rededication to the proposition that hard work and sacrifice became worthwhile, not only because of the resulting self satisfaction, but also because the man beside you was working just as hard as you were. This feeling of family made every member take pride in the accomplishments of individuals: Jolene Miller-O'Toole was named Color Guard Captain of the Year by Drum Corps World.

The corps had the honor of playing for President Jimmy Carter while he was traveling down the Mississippi River on the Delta Queen in 1979.

In 1980 the Robert M. Buelow Award was established to honor Bob for his 17 years of service to the corps; it is awarded each year to the person who "contributed leadership, loyalty and personal commitment to the Colts Drum and Bugle Corps during the preceding years."

In 1981 the Colts sponsored a movie premiere ("Take This Job and Shove It") and a circus (for which the 32,000 brochures announced that sponsorship was by the 'Colts Drug & Bugle Corps'), and they purchased three used buses, promptly dubbed the Poseidon, the Lusitania and the Titanic. Although they had toured extensively for years, 1981 was the first year the corps made two tours.

The 1982 Colts can be considered a turning point in the corps' history. An influx of new members helped the corps strengthen its family atmosphere and audience oriented shows. At the DCI Championships in Montreal the corps reached its goal of Associate Membership with an historic 24th place finish, their highest placement ever.

The Colts innovated the complete show design for the first time in drum corps history in 1983 with the 'Mississippi Suite,' using different songs and props to tell a continuous story throughout the entire show. At a North Carolina show the crowd, feeling the Colts should have won, booed their second-place finish. This helped members understand that numbers and placement are less important than how they as individuals felt after a performance.

In 1984 the Colts became the "Kings of Swing,“ fielding drum corps’ first trap set. At the end of the season, after seven years as director, Jim Mason left to become the director of the new Star of Indiana, and Greg Orwoll, the corps’ director for more than 15 years, took over.

After their 16th place finish in 1985, Governor Terry Branstad proclaimed the corps "Iowa's Ambassadors of Music,” and jazz ruled the repertoire. The jazz style continued into 1989 with the largest hornline in corps history, 54 members. A record eight foreign musicians traveled to Dubuque to be a part of the 1985 Colts.

1991 saw the restructuring of the member responsibilities and approach to rehearsing and performing, while still keeping the focus of the corps values of entertaining the audience, educating the members and supporting the corps family. During this period the Colts changed their repertoire from jazz to new age literature.

As part of the corps’ 30th anniversary celebration in 1993, they sponsored a parade in conjunction with the local community theatre's production of "The Music Man;” grand marshal was Mrs. Meredith Willson. The corps that performed in the evening show participated in the parade, which was televised live and attracted the largest crowd to witness a parade in Dubuque in modern times.

The modern day Colts Alumni Association and the Colts Hall of Fame were established in 1993. The Hall of Fame recognizes those who have been a vital part of the Colts history.

The Colts thrived in the heat and humidity of Jackson, Mississippi, in 1993, and surprised everybody with a 12th place DCI finish after years of finishes in the twenties. They stayed in the top 12 through 1996. The directors of Drum Corps Midwest voted them the Most Improved Corps Award, and DCM awarded Greg Orwoll Director of the Year honors. The Colts' best ever finish was ninth, in 1995.

The corps started defining the Colts Style in 1998 with the 'A Capella Show,' placing greater emphasis on marching and technique. An incident that year helped the Colts family knit more tightly, and reaffirmed the family of drum corps itself. On the way to a show in Montreal, the three buses were in an accident. Six people went to the hospital, while the rest of the corps went to the stadium. All of the other corps helped the Colts regain their footing, donating food, buses, and time that night. The members and staff pulled together, and the family was made tighter.

In 1998, in Orlando, the Colts regained their top 12 standing with a twelfth-place finish, creating momentum that carried into 1999. The Colts Style became even more evident that year, both on and off the field. The group's cornfield pratcie field was extended to give the corps a chance to get the show completely on the field, even though record Midwest heat forced them to rehearse at night. Their travels took them to Washington, D.C., where they performed at the U.S. Capitol, and the drum majors participated in a ceremony at The Tomb of the Unknown Soldier. And at the Madison DCI Championships, the corps found themselves with a World Champion cymbal line, which scored of 97 out of 100.

After a large age-out, the corps was full of mostly new staff and membership (average age 17.5) in 2000, creating an energetic atmosphere. The show, entitled 'The Wait of the World,”'was also one of the most demanding and ambitious Colt performances, encouraging a well-deserved competitive leap. But Semifinals were as close as the corps would get, with a 14th-place finish. The 2000 banquet was hosted in the new Colts Community Center, the first property the corps has owned.

With most of the staff and members returning in 2001, it was easy to pick up where the 2000 corps left off. All season, the Colts were performing at a higher level than had been reached in previous years. On Semifinals night, the corps placed 12th, sending them back for a Saturday night at Finals. This was an experience that many members of the corps had yet to share, making the evening that much more special. Overall, the corps grew as a family and matured as a performing organization.

In 2003, their 40th year, the 122-member Colts finished 16th in DCI Semifinal competition with a beautifully harmonic show entitled 'Symphonic Visions.'

The corps from Dubuque performed a American program called 'From the Heartland' in the heartland at Denver to a second consecutive 16th-place finish in the 2004 DCI Semifinals.

[http://www.colts.org/history.html; DCW, 5/02, p.3; DCW, 6/8/90, p.2]