One of my students recently asked me to describe the difference betweenin and on?  Since these are two of the most commonly misused prepositions in English, I figured it would be a good topic for this week’s column.  In and on are used to talk about either a period of time or a place that something happens.
If you are referring to a month, year, season, or general period of time, you will use the word in. For example:
 I will graduate in May
 She was born in 1974
 The pool will be open in summer.
 I will meet you there in one hour.
If you are speaking about a specific day, date, or Holiday, you will want to use the word on.  The following are some examples:
 I have a doctor appointment on Thursday 
His birthday is on September 12th.
 She loves to dress up on Halloween.
When talking about a town, province, city, state, or country, you will use in.  However, if you are talking about a street name, be sure to use on.  Again, here are some examples:
 I live in Denver, Colorado.
 He is vacationing in Hawaii.
 My house is on Main Street.

The word in can also be used when an someone is inside or contained in something else. While the word on generally means that they are above or outside of an area, as in the following sentences:
I am in trouble
 The hammer is in the toolbox
 I like to ride on my bicycle.
 
Practice:
Complete the sentences by filling in the blank spaces with either in or on.

Molly Brown was born ___ Hannibal, Missouri ___ July 18, 1867.
___ September 1, 1886, she married James Brown.
They lived ___ Leadville, Colorado, where Mr. Brown made his fortune by mining.
___ 1912, Molly Brown was a passenger ___ the RMS Titanic.
She was ___ one of the lifeboats that was rescued, giving her the name, “The Unsinkable Molly Brown.”