We know hockey was popular enough in New York, Boston, Chicago and Detroit to support NHL teams. But outside of these cities, did professional hockey have much of an American fan base? Were the Stanley Cup playoffs nationally broadcast on TV or radio? Would the average person in, say, Nebraska have any idea who Gordie Howe or Rocket Richard were?
In short, it varied by region. The NHL had a national TV deal with CBS that lasted from the mid-1950s until the early 1960s, and the desire to once again be broadcast nationally in part led to the 1967 expansion.
There was also a strong minor league system throughout the US at this time, with the American Hockey League based in the northeast US and the Western Hockey League (not the current junior league) stretching down the west coast. Several teams in both leagues were extremely popular, and with only 6 NHL teams they were full of good players: the Cleveland Barons of the AHL even applied to both join the NHL or play for the Stanley Cup in the 1950s, though both offers were declined.
The WHL in particular merits note; it had several strong teams and in the mid-1960s began discussing turning into a major professional league, on par with the NHL. This was probably the biggest factor into the NHL deciding to expand (along with the aforementioned TV deal): note that both Los Angeles and San Francisco, cities that were given NHL teams in 1967, had previously housed WHL teams.
So its possible someone in Nebraska would have heard of Howe or Richard, but they likely didn't get to see them play (though worth pointing out that Howe spent the 1945-46 season with the Omaha Knights, a minor league team affiliated with the Red Wings), but they would have been mentioned in newspapers, and the local minor league team would have been more likely to be followed.