Around 175 in 1973 at a district in west-central NH that probably had a total population of between 10,000 and 12,000.
My Wife experienced similar numbers a few years later in east-central NE.
My kids went to high schools with classes in excess of 600, Millard North and Millard West high schools in suburban Omaha.
The current population in the Omaha metro area is between 800,000 and 900,000, more than the entire population in each of the following State; AK, ND, VT, and WY, so you'd expect a lot of big high schools. Omaha Public Schools have more than 50,000 students.
