A character in Designated Survivor talked about how someone was sentenced to 60 or 70 years, noting how it was ten times the length of the average sentence for a murder at the same time period. I feel like the average sentence wouldn’t have been so radically reduced so recently. Is there a database for average sentence lengths for specific crimes by year or decade?
The short answer: Depends on severity. Felons convicted of murder are sentenced 25 years to life, and possibly no chance for parole if sentenced to life. Death penalty is very rare (if it isn't banned in the location) and reserved for the worst murder cases. In the old days before widespread prisons, felons were just hung. As prisons became more and more "popular," prison sentences became more and more common and the death penalty became rarer and rarer. Also, lots of paywalls to get National Archive information. Lots of them.
The long answer that goes off-topic:
As far as I know, there is no website that shows a nice graph of average sentence lengths per year on the Internet. The reason is because the sentence length varies so much depending on the circumstances.
All of the information below is based off California's laws. Other states have similar, if not identical laws.
California recognizes two types of murder: first degree and second degree murder. Second degree murder is killing someone. Sentences for second degree murder last about 15 years, and is in a state prison. First degree murder is when one or more of the following are met:
[It] is accomplished by means of a destructive device, weapon of mass destruction, armor-piercing ammunition, poison, lying in wait, or torture; or
is done in a way that is willful, deliberate and premeditated; or
invokes the California felony murder rule because the murder occurs during the commission of certain serious felony crimes.
[Source]
The punishments for first degree murder are much stricter. Sentences can last anywhere 25 years to life, and possibly without parole. In extreme cases, murderers can be sentenced to death, but California has suspended the death penalty (and so have many other states).
I would imagine the sentence for murder has been similar as long as prisons have been around. The only difference is the use of the death sentence has gone dramatically down, with states such as California suspending the death sentence. The reasons for this are most likely the increase in large prisons over the course of the last 200 years and the increase of the opinion that the death sentence is not good in the general population.
EVERYTHING BELOW IS THE HISTORY OF PRISONS AND HOW FELONS WERE TREATED. IT IS PROBABLY OFF TOPIC IN SOME WAY, BUT STILL RELATED.
As for early England, I can point you to this booklet by the University of Michigan Law School for more information on what was murder. Skip to 436 for the kind of murder we are familiar with (called "Justified Murder"). It is too confusing for my little brain.
During the 1800s, punishments were determined by the severity of the crime.
Felonies defined by common law were originally punishable by hanging, but increasingly from the middle of the eighteenth century, statute law curtailed the use of the death penalty. Misdemeanours were punishable by a range of non-capital punishments. Normally, offences defined by statute could only be punished as prescribed by the relevant legislation. The punishments available in any particular case were thus circumscribed by the legal status of the offence with which the defendant was charged.
[Source]
However, people were often charged of multiple crimes because the Jury manipulated the laws and finding partial crimes to make the punishment more severe. Murderers would often be hung. It was not until 1779 in Britain when the Penitentiary Act, which authorised the building of prisons. The first prison as we know today opened in 1816 in Millbank.
People started to move further and further away from the idea of killing felons. The death penalty became rarer and rarer. Prisonment became a more and more popular choice for punishments.
Surprisingly, I have not found information on how long the prison sentence during the early 1900s was. If you want to know how long, you might have to do some digging in the National Archives, examine how long the prison sentence was for a murder case, compare it to other murder cases, and you would have your answer. I tried looking online but found only dead-ends and paywalls. Visit the national archives or something.