Charles G. Conn was a Civil War veteran of the U.S. Army who, after the war, established a grocery and baking business in Elkhart, Indiana. He also played cornet in the local community band. Conn's entrance into the musical instrument manufacturing business was the result of a split lip. There are three existing stories of how this occurred, but the popularly accepted version is that Del Crampton slugged him in the mouth outside a saloon where both of them had been drinking. Conn's upper lip was severely lacerated, and it pained him so to play his cornet that he thought his playing days were over. In addition to running his store, Conn also made rubber stamps and re-plated silverware. He decided to try adhering rubber stamp material to the rim of a mouthpiece which he hoped would conform to his lips. After he showed his friends his idea, he realized that there was tremendous demand for his invention. Conn then began to contemplate manufacturing his new mouthpiece. He needed a rim with a groove which the rubber cement would adhere to more easily. It was in 1874 when Conn converted a discarded sewing machine frame into a simple lathe and started to turn out his mouthpieces and was soon in full production (Subsequently, Conn and Del Crampton became best of friends, and when Conn embarked on his political career, he was a staunch advocate of temperance). Conn patented his rubber-rimmed mouthpiece in 1875 (with patents to follow through 1877) described as "an elastic face [i.e., a rubber rim] where the mouthpiece comes in contact with the lips, the object being to prevent fatigue and injury to the lips."

Conn met Eugene Victor Baptiste Dupont, a brass instrument maker and designer and a former employee of Henry Distin of London. In January 1876, Conn joined with Dupont under the name of Conn & Dupont, and Dupont created Conn's first instrument, the Four-in-One cornet, with crooks allowing the horn to be played in the keys of E♭, C, B♭, and A. By 1877, Conn's business had outgrown the back of his grocery store, and he purchased an idle factory building on the corner of Elkhart Avenue and East Jackson. Conn's partnership with Dupont was dissolved by March 1879, but he was successful in attracting skilled craftsmen from Europe to his factory, and in this manner he expanded his operation so that by 1905, Conn had the world's largest musical instrument factory producing a full line of wind instruments, strings, percussion, and a portable organ. Conn partnered with Albert T. Armstrong, Joseph Jones, and Emory Foster to manufacture a twin-horn disc phonograph called the 'Double-Bell Wonder' that was produced in two iterations briefly in early 1898 before a lawsuit by the Berliner Gramophone Company caused production to cease. Brick-red 'Wonder' records were also pressed for the 'Double-Bell Wonder' talking machine by the Scranton Button Works from pirated Berliner masters. Fewer than fifty 'Double-Bell Wonders' were produced of both iterations combined.

Conn's first factory was destroyed by fire on January 29, 1883 (his thirty-ninth birthday), and he erected a new building on the same site. In 1886 rumors began to circulate that Conn wanted to move his business to Massachusetts. Conn was induced to stay after the public raised a large sum of money by popular subscription and gave it to him. In 1887 Conn purchased Isaac Fiske's brass instrument manufactory in Worcester, Massachusetts, upon Fiske's retirement. Fiske's operation was considered to be the best in its time. Conn operated it as a company subsidiary, and in this way he achieved his objectives. The company's product line now centered on the 'Wonder' cornet, but in 1885 Conn began importing French clarinets and flutes. Conn prototyped the first American-made saxophone in 1888, after being shown an Adolphe Sax saxophone by his employee Ferdinand August Buescher and agreeing to produce a copy of it. That instrument belonged to Edward A. Lefebre, a well known soloist with both Patrick Gilmore's and John Philip Sousa's bands. After working on prototypes with advice from Lefebre, Conn settled on production models of saxophones and started regular production around 1892.^[1] Conn's instruments were endorsed by several leading band directors, including Sousa. In 1898, on the suggestion of Sousa, Conn developed the first commercially successful bell-up sousaphone ("the rain-catcher"). Conn phased out the Worcester operation (closed in 1898), and Conn established a store in New York City (1897–1902) that sold a large variety of merchandise under the 'Wonder' label, including Conn-made woodwind, brass and percussion instruments, violins, mandolins and portable reed organs. The business also distributed American-made and imported guitars, banjos and zithers.

Conn's marketing included not only sales of instruments but promotion of brass bands. He founded the Conn Conservatory to train the brass instrument teachers who would be a vital component in the growth of the musical instrument industry. During the 1890s E.A. Lefebre started teaching saxophone at the Conservatory, which provided a boost to the availability of saxophone instruction and the following growth of saxophone sales into the twentieth century.

Conn's company was a source of competitors as well as instruments. Notable employees who left the firm to pursue their own businesses were composer W. Paris Chambers, the founder of the Seidel Band Instrument Company William F. Seidel, the founder of the Buescher Band Instrument Company Ferdinand A. Buescher, the founder of the F.E. Olds Company Frank E. Olds, the founder of the Martin Band Instrument Company Henry Charles Martin, and William Gronert and Harry Pedler, who would go on to form AMC (American Manufacturing Company) in 1916, which re-organized as Harry Pedler & Co., after Gronert's death in 1919.

Conn's second factory burned on 22 May 1910, a loss estimated between $100,000 and $500,000. Conn was en route from California to Elkhart when his factory burned, and upon arriving home he was met with a public demonstration, a way of showing popular sympathy. Conn then announced his intentions to build a third factory on the corner of East Beardsley and Conn Avenues. Construction began 15 August 1910, and by the following 12 December it was fully operational.^{[citation needed]}

Conn's career grew well beyond the realm of musical instrument manufacturing. In 1892 he was elected to the United States Congress, in 1908 he ran for Governor of Indiana and lost, and in 1910 he ran for Senator. In 1889, Conn founded the Elkhart Daily Truth, published the monthly Trumpet Notes and a scandal sheet called The Gossip, and purchased The Washington Times, which he later sold. After a failed entry into the utilities business, the building of his third factory (and its loss to fire), and his loss of a costly lawsuit filed against him by a former company manager, Conn had amassed significant debts. In 1911, in an effort to bond Conn's debts and secure working capital, Conn and his wife executed a trust deed for $200,000 covering not only the horn factory, but all their possessions, with the longest bond to mature in ten years. Conn's growing debt crisis forced him to seek a buyer for his assets, and in 1915 all of Conn's holdings, including the horn factory, were bought by a group of investors led by Carl Dimond Greenleaf, whom Conn had met during his years in Washington, D.C.

Carl Greenleaf was president of Conn from 1915 to 1949. The new company was incorporated with public stock offerings under the name C. G. Conn, Ltd. and the Conn trademark was updated to the official name of the new company.^[2] Greenleaf was an astute businessman, sensitive to the market trends of the industry. While president, Greenleaf noted the gradual decline of the small town brass band, and of the big touring bands such as the Sousa band. To shore up the future market for band instruments, he undertook to promoting band programs in schools and colleges. He proceeded to develop a close relationship and communications between the industry and music educators. His collaboration with educators such as Joseph E. Maddy and T.P. Giddings helped introduce band music into public schools. Greenleaf organized the first national band contest in 1923 and helped make possible the founding of the National Music Camp at Interlochen, Michigan. In 1928 he founded a Conn National School of Music which trained hundreds of school band directors, and this in turn helped spur the development of music programs in schools and communities across the United States.

Under Greenleaf's leadership the company converted distribution from mail-order to retail dealers and expanded its product line through acquisitions. C. G. Conn founded the Continental Music retail subsidiary in 1923 which, at the height of its success, included a chain of over 30 music stores. During the 1920s C. G. Conn owned the Elkhart Band Instrument Company (1923–27), the Leedy Company (1929–55), a manufacturer of percussion, and 49.9% of the stock of the retailer H. & A. Selmer (1923–27). Conn purchased the drum manufacturer Ludwig and Ludwig, the instrument import/retail operation of the Carl Fischer company, and accordion manufacturer Soprani in 1929. From 1940 to 1950 the company owned the Haddorff Piano Company, and from 1941 to 1942 the Straube Piano Company.

Greenleaf expanded and upgraded C. G. Conn's plant to increase production and developed new lines of wind instruments to sell. By 1917, using a new hydraulic expansion process which Greenleaf introduced to the plant, the assembly-line work force had increased to 550 employees who were turning out about 2500 instruments a month.^{[citation needed]} In 1917^{[citation needed]} C. G. Conn introduced the Pan American brand for its second-line instruments, forming the Pan American Band Instrument Company subsidiary in 1919 and moving production of second-line instruments to the old Angledile Scale factory, which had been transferred to the new company among Conn's other assets, later that year. In 1930 the Pan American company was absorbed by C. G. Conn, with Conn retaining and utilizing the Pan American brand for its second-line instruments until 1955.

By 1920 C. G. Conn was producing a complete line of saxophones. In this area they had competition from other big saxophone makers such as Buescher and Martin. Around 1917 C.G. Conn introduced drawn tone holes (a feature patented by W.S. Haynes in 1914) eliminating the process of soldering tone holes onto the bodies of the instruments. Around 1920 C. G. Conn introduced rolled tone hole rims, a feature that enhanced the seal of the pads and extended pad life. Rolled tone holes remained a feature of Conn saxophones until 1947. By the late 1920s the success of Conn's latest "New Wonder" model saxophones with dance orchestras was gaining widespread attention, leading European manufacturers to produce horns closer to the deeper, richer, bolder "American" sound.^{[citation needed]} Selmer (Paris) introduced the American-sounding "New Largebore" model in 1929 and the new Julius Keilwerth Company in Czechoslovakia produced saxophones influenced by the C. G. Conn design, including rolled tone holes and microtuners. As sax sales plateaued in 1928, Conn introduced a mezzo-soprano saxophone in the key of F and the "Conn-o-sax", a saxophone-English horn hybrid, but these instruments were soon discontinued after disappointing sales.

In 1928, under the direction of Carl Greenleaf's son Leland Burleigh Greenleaf, C. G. Conn opened its Experimental Laboratory, which was unique in the industry. Under Leland Greenleaf's directorship, the department developed the first short-action piston valves (1934), and the 'Stroboconn' (1936), the first electronic visual tuning device. It also developed the "Vocabell" (1932), a bell with no rim, which C. G. Conn described as "vibrat[ing] freely and in sympathy with the vibrating column of air in the instrument,"^[3] C. G. Conn also developed the "Coprion" bell (1934), a seamless copper bell formed by directly electroplating it onto a mandrel. Under Greenleaf's saxophone specialists Allen Loomis and Hugh Loney, C. G. Conn's research and development resulted in the designs of the 6M alto (1931), 10M tenor (1934), 12M baritone (1930), and 14M bass (1930). The 12M baritone and 14M bass were the first saxophones to have both bell keys on the right side. The 6M alto featured an innovative double socket neck that eliminated the large collar on the body tube at the neck joint for a more positive seal and even response, later adopted by some other manufacturers. From 1935 through 1942, C. G. Conn produced the 26M and 30M "Connqueror" alto and tenor saxophones, featuring screw-adjustable keywork and improved mechanisms for the left hand cluster. The keywork was the most fully adjustable of any saxophone during that period. C. G. Conn's labo