According to Wikipedia which is always a reliable source..
Like all such musical genres, defining a single point of its development is difficult, as many elements of disco music appear on earlier records (such as the 1971 theme from the movie Shaft by Isaac Hayes). In general it can be said that first true disco songs were released in 1973, however, many consider Manu Dibango's 1972 "Soul Makossa" the first disco record.
1966–1974: Early history
The disco sound, style and ethos has its roots in the early 1960s, as record hops and radio DJ's began to replace live bands with recorded music. Discos were first popular in Europe (where the term "Discotheque" was initially coined) and quickly spread to America.
New York City Blacks, gays, heterosexuals, women, Hispanics and Italians adopted several traits from the hippies and psychedelia. They included overwhelming sound, free-form dancing, "trippy" lighting, colorful costumes, and hallucinogens.Psychedelic soul groups like the Chambers Brothers and especially Sly and The Family Stone influenced proto-disco acts such as Isaac Hayes, Willie Hutch and the Philadelphia Sound. In addition, the positivity, lack of irony, and earnestness of the hippies informed proto-disco music like M.F.S.B.'s "Love Is the Message".
Philly and New York soul were evolutions of the Motown sound. The Philly Sound is typified by lavish percussion and lush strings, which became a prominent part of mid-1970s disco songs. Early songs with disco elements include "You Keep Me Hangin' On" (The Supremes, 1966), "Only the Strong Survive" (Jerry Butler, 196
, "Message to Love" (The Jimi Hendrix Experience, 1969), "Soul Makossa" (Manu Dibango, 1972), "The Love I Lost" (Harold Melvin & The Blue Notes, 1973) and The Intruders "I'll Always Love My Mama" (1973).
From 1974 through 1978, Disco music continued to increase in popularity as many disco songs topped the charts. The Hues Corporation's 1974 "Rock The Boat", a U.S. #1 single and million-seller, was one of the early disco songs to hit #1. Other chart-topping songs included "Walking in Rhythm" by The Blackbyrds, "Rock Your Baby" by George McCrae and "Love's Theme" by Barry White's Love Unlimited Orchestra. Also in 1974, Gloria Gaynor released the first side-long disco mix vinyl album, which included a remake of The Jackson 5's "Never Can Say Goodbye" and two other songs, "Honey Bee" and "Reach Out (I'll Be There)".