The United States Hockey League is a Junior hockey league that has operated in this format since 1979. It is currently classified as a US Junior A Tier I hockey league, which is the highest junior hockey category in the US, and is currently the only league in that category in the US.
The USHL has a very unusual lineage; it is the byproduct of a 1970's merger between the NHL-supported Midwest Junior Hockey League and the semi-professional United States Hockey League which had existed in various incarnations since the 1940's. The two leagues started their relationship by playing an interlocking schedule in 1976-77. The leagues then merged for the 1977-78 season, keeping the USHL moniker but playing in a United States division (senior teams) and Midwest Division (junior teams). The league shifted even more to an all-junior format the following season, with younger players assuming more roster spots on the senior teams. In 1979-80, the USHL moved to an all-junior format.
... [Click for more]r />Although the USHL has always promoted itself as a path to play college hockey, and though there were some instances of players making this transition, for the first few years under the junior-only format the majority of players did not move beyond the USHL. Most of the players were drawn from the midwest; the USHL did not yet have a national reputation.
However, the league persevered, and over time more and more of its players wound up on NCAA college rosters and a good deal of those players wound up playing professional hockey, many reaching the National Hockey League. With more players achieving this goal, the league's stature grew and it began to attract better talent from across the United States. The league is now considered the top Junior hockey league in the United States, and many consider it to be approaching the stature of the Canadian Major Junior Hockey Leagues. The one big difference is that the USHL remains a pure amateur league - players are not compensated in any way, so they retain their NCAA eligibility (the Canadian Major Junior leagues pay players small stipends, which eliminates their NCAA eligibility).
Although it has branched out somewhat from its fouding region of Minnesota/Wisconsin/Iowa, The USHL has generally remained in its historical geographical footprint in the US Midwest and over the past few years has picked up teams in cities that were once members of professional hockey leagues such as the IHL or CHL.