Why do I have to use "the" before "hospital" but not before "jail" as in:
He went to the hospital before he went to jail.

In the UK, I believe the most common usage omits "the" before
"hospital." I've often seen sentences such as "I visited him in
hospital."

Well, if "jail" were replaced with "shopping mall" in your example,
you would use "the".

So, might it have something to do with "going to jail" being a phrase
which generally expresses "being incarcerated" - as opposed to "going
to the jail" which would indicate a specific building?

Thither,
Your coment is absolutely correct:  the difference is between the
meaning of jail (or hospital in the UK) as an expression of the
person's being incarcerated or hospitalized, versus the suggestion of
an unnamed specific jail (goal in UK) or hospital.

In Pink's example, "in hospital" clarifies that the visit wasn't "at
home", the usual assumption in connection with "visit".

Thither-ga and myarin-ga are correct.

Furthermore, in the north-west of England the word "the" is often
omitted, and it would not be uncommon to hear "I went t' beach" for "I
went to the beach".

I think it may be to do with the intent of meaning.

1. "I am going to the hospital" meaning "Just visiting"
2. "I am going to hospital" meaning "Being admitted"

I think the same applies to jail.

Mind you where I come from we usually add up or down to 1.

"I'm goin' up to the hospital"
"I'm goin' down the shops"

Cheers

No, I disagree with the 5 prior commentators.

You don't have to use the word "the" before "hospital" in your
sentence unless you desire to do so AND it is relevant to both you and
the person to whom you are speaking or writing. It depends on the
personal context of both the speaker and the hearer.

The word "the" is also known as the "definite article". If you wish to
understand the grammar of the word "the" then a google search using
the phrase "the definite article" or the phrase "definite article"
will produce many good results.

I liked this explanation sourced from "UsingEnglish.com"
'The' is the definite article is English. It is used to restrict the
meaning of a noun to make it refer to something that is known by both
the speaker or writer and the listener or reader.
'He's gone to the shops' (Here the listener knows which shops I mean)...

Note that the words "a" and "an" are known as the "indefinite article".

So if I hear you say to another person "He went to the hospital before
he went to jail." I will naturally assume both you and the person to
whom you are speaking have a common knowledge or a shared
understanding about which particular (definite) hospital you are
referring to but that with respect to the jail you may or you may not
(it's indefinite) have a common knowledge about which jail is referred
to.

Further if by inserting the word 'a' into the sentence before 'jail'
it becomes "He went to the hospital before he went to a jail." I would
now be certain that with respect to the jail you and your listener had
no common knowledge or shared understanding about which jail and that
as the speaker you yourself may not even know which jail.

Now try this. The other day my spouse said to me "Please wash the
dirty dishes." So I went to the kitchen and washed every dirty dish
and pot I found on the sink and benches. The next morning my spouse
said "Why didn't you run the dishwasher? I thought I asked you to wash
the dirty dishes." The problem - my spouse thought the particular
dishes was definite and I thought they were definite but we lacked a
common knowledge or shared understanding about which dishes!!!!!

Going to jail is like going to work or going to school.  A lot like, in fact. 

It's not like going to the store or going to the beach or even going to the moon.

You go to sea and to the ocean.  To work and to the office.  To town
and to the city.  To college and to the university.

Maybe one is abstract and the other concrete, but I think it's just idiom.

Tryx

Hmm, well, I thought an idiom was words used to in a sense not
implicit in their normal meaning.  "Kick the bucket" seems to be a
favored example.

A nice selection of other examples of usage without an article, though.

Ponder,
That is all fine and correct and expands on the usage of articles, but
it doesn't deal with the question of the difference in meaning if no
article is used.

A few final thoughts on this topic (please note that I am using
American English in my examples):

The cases where the article may be omitted are, it seems to me,
instances where there is more is being expressed than the simple
process of going someplace. I guess you could call them minor
idiomatic expressions/shortcuts in that they are not fully literally
translatable.

For instance, going back to the original "jail" - here are three
statements with their equivalent meanings:

"I'm going to the jail." = I'm going to pay a visit to some specific jail.
"I'm going to a jail." = I'm going to pay a visit to some non-specified jail.
"I'm going to jail". = I'm going to pay a visit to some non-specified
jail AND I'm going to be locked up.

Obviously, there are many place nouns where the article can't really
be omitted - I can't say that I'm going "to bookstore" or "to
supermarket" or "to topless car wash" without the listener thinking
that that was a bit of an odd sentence.

It seems to me that the other cases where the article may be omitted
also contain an additional meaning beyond simply going someplace:

"I'm going to church" - not just going to that place but also attending services
"I'm going to school" - not just going to that place but also being
involved in the educational process
"I'm going to sea" - not just going to that place but additionally sailing 

I think there might be a few more examples (like work and war although
these are also verbs).

So, going someplace vs. going someplace and something happening (at
least that's my take).

I hope this helps.

Have a good day.

Thither, I agree with you. Our answers are consistent.

Carlitosintx originally asked the question - "Why do I have to use
"the" before "hospital" but not before "jail" as in: He went to the
hospital before he went to jail."

Carlitosintx, in direct response to your question, in the English
language you do not have to use "the" before the word "hospital" and
you are not stopped from using "the" before the word "jail".

Each of these 7 sentences are perfectly correct but each conveys a
slightly different meaning. You will use or not use "the" and "a"
depending on the particular meaning you wish to convey:
He went to the hospital before he went to jail.
He went to hospital before he went to jail.
He went to hospital before he went to the jail.
He went to the hospital before he went to the jail.
He went to the hospital before he went to a jail.
He went to a hospital before he went to a jail.
He went to a hospital before he went to the jail.

Here is another reference found via Google for extended understanding:
"The Use and Non-Use of Articles" From the "Online Writing Lab (OWL)
at Purdue University
http://owl.english.purdue.edu/handouts/esl/eslart.html