This post starts with the most common use of the three prepositions, followed by other usages. Wherever possible, the prepositions have been presented in tabular form for ease of comprehension. Comments are in square brackets in blue font so that you can easily spot them. And the post ends in a quiz for you to test yourself.

Let’s start with the most common use of the three prepositions.

1. The most common use of At, On, and In

AtOnIn
At is used to describe a place when you think of it as a point rather an area.On is used to describe a position touching a flat surface.In is used to describe: (1) a position within a larger area [In a stadium/ city/ country]; (2) something within a larger space (three-dimensional) [In a box/ bag/ room/ building]
Examples
I saw a vendor selling fruits at the bus stop.There is a lizard on the wall/ ceiling/ floor.There were more than 200 persons in the hall/ city center.
Can you check who is at the door?He is sitting on the chair/ grass/ lawn/ beach.We’ve barely identified one percent of all species in our oceans.
He is working at his desk.John is sitting on the garden. [Showing position touching a surface]X: Where is John? Y: He is in the garden. [Showing position within a larger area]
The post office is located at the end of the road.The mangoes on the tree have ripened and can fall if not plucked.I had a swim in the river/ sea/ lake.
Write the date at the top of the page and your name at the bottom.There is a notice on the wall requiring your presence in the court next week.What’s in that box/ bag/ cupboard?
Can you please leave my book at the hotel’s reception?Can you put this painting on the wall?New Delhi is in the north of India.
Go straight and take a left turn at the shop.There is a label on the bottle.I like to look at the stars in the night sky.

2. Other use of At

We say somebody is at home/ at work/ at school/ at university/ at college/ at station/ at airport etc.:

Examples

I’ll be at home 6 PM onwards.

I’m at work even on Saturdays.

I’m studying science at college.

At my sister’s place.

I was at my friend’s house last night. [We say ‘rooms in my friend’s house are spacious’. See subsection 5.4 further down in the post to know why]

I was at the doctor’s clinic this morning.

I’ll now see you directly at the station.

We say somebody is at an event/ at a party/ at a conference etc.:

Examples

I last met him at the solar energy conference.

There were just nine persons at the party.

I saw him at the concert yesterday.

He called me up when I was at the football match.

Only two showed up at the meeting.

3. Other use of On

On the left/ right:

Examples

He was driving on the right side (the wrong side) when the accident happened.

I sit on the left of my best friend in the class.

On the ground (first etc.) floor:

Examples

I live on the ground floor of a high-rise building.

There is a pool and parking on the fourth floor of the building.

On a map/ on the menu/ on a list:

Examples

What’s new on the menu?

How many invitees are there on your list?

On a farm:

Examples

I injured my leg while moving the harvester on the farm.

We use on to describe the location of a place on something in the form of a line (road, river etc.):

Examples

New York City is on river Hudson.

My school is on the main road.

Los Angeles is on the West Coast of U.S.

We say that a place is on the way to another place:

Examples

We stopped at a dilapidated mud house on the way to our first-day halt on the trek.

4. Other use of In

In a line/ row/ queue/ street:

Examples

I sit in the second row in my class.

I’ve been in this queue for the last 30 minutes.

His office is in AL Street.

In a photograph/ picture/ mirror:

Examples

Where are you in the photograph/ picture?

Did you look in the mirror today? There is a swelling under your left ear.

In a book/ newspaper/ magazine/ letter [But: on a page]:

Examples

I read about your accident in the newspaper.

I was referring to the picture on page 23.

We say somebody is in bed/ hospital/ prison:

Examples

It’s 8 in the morning, but he is still in the bed.

He has had a major surgery and is expected to be in the hospital for at least five more days.

He has been in the prison for last three years.

We say someone works in a shop, bank, factory, store etc.:

Examples

I’ve been working in this factory for two years now.

My brother works in a bank.

5. More…

5.1 The corner

We say in the corner of a room, but at the corner or on the corner of a street:

Examples

There is a grocery shop at the corner of the street.

The chair is in the corner of the room.

5.2 The front and the back

All three – at, on, and in – can be used depending on the usage.

AtOnIn
We say at the front (or back) of a building/ cinema/ group of people etc.We say on the front (back) of a letter/ piece of paper etc.We say in the front or in the back of a car.
Examples
Let’s sit at the front of the class/ cinema.Write your address on the front of the envelope.Let’s sit in the front row.
I was standing at the back during the group snap.Write your phone number on the back of the cheque.The guy sitting in the front on the car suffered fatal injuries in the accident.

5.3 Address, streets, and roads

AtOn/ In
At is used before an address.However, in or on are used before the name of a road.
Examples
They’ve opened a showroom at 26 MG Road.They’ve opened a showroom on/ in MG Road.
I live at 12 Walnut street.The town is on Grand Trunk road. [On is preferred when describing long streets or roads]

5.4 Buildings

AtIn
We usually say at when we say where an event takes place.We use in when we describe the building itself.
Examples
The meeting took place at the company’s headquarters in Singapore.The rooms in Raffle’s Tower, the company’s headquarters, are quite small.
The movie is showing at Odeon.It was quite cold in the cinema hall.

Quiz

Fill in the blanks with the preposition of place at, on, or in.

1. There is a fly ___ the bottle.

2. We went to the concert ___ South Hall.

3. There is notice ___ the door. It’s a summon from the court.

4. Few passengers have been stranded ___ the island since yesterday.

5. This Sunday, I’ll be ___ my brother’s place.

6. I bet there are at least 20 persons ___ the shop.

7. My father’s office is ___ river Narmada.

8. As per protocol, you need to write your address ___ the top of the letter.

9. I came late for the movie. I had to sit ___ the front row.

10. I always sit ___ the front in my class.

1. on   2. at   3. on   4. on   5. at   6. in   7. on   8. at   9. in   10. at