on summer holidays I went vs in summer holidays I went

Some examples from the web:

• I went to Bali on summer holiday.
• Mr President, last summer I went on holiday to Guinea-Bissau, and, as is my wont, I exchanged a few words with one of the local elderly pensioners, or rather with a fisherman from Guinea-Bissau would have dearly loved to have become a pensioner.
• They paid their fines, gave some interviews and towards the end of the summer they went on holiday.
• I hope that before the summer holiday I will be able to submit a formal motion to make their agreement binding.
• No, he's been away on summer holiday.
• He never married, worked as an engineer for may years, and when he retired he decided to live in Araruama, a city near Rio de Janeiro. That is where the whole family went to spend the summer holidays with the children.
• Like when you change schools, or end the summer holidays.
• No matter how hard it is, you can't come home until the summer holidays.
• I can't wait for the summer holidays.
• It was on my summer holidays.
• Come and see me in Tokyo in your summer holidays.
• Come and see me in the summer holidays.
• Our aim is to present a revised proposal after the summer holiday.
• Some 200 million Europeans chose a destination with recreational water for their summer holidays.
• Not just a summer holiday or visit...
• I decided to start my summer holidays earlier.
• It's summer holidays, Mrs Rogers.
• (Gandini) here and spent the summer holidays surrounded by his friends.
• You indicated that this might be ready by August, which misses this year's summer holiday period.
• The workers suspect that the factory will be closed down after the summer holidays.

Some examples from the web:

• Mr President, last summer I went on holiday to Guinea-Bissau, and, as is my wont, I exchanged a few words with one of the local elderly pensioners, or rather with a fisherman from Guinea-Bissau would have dearly loved to have become a pensioner.
• I went to Bali on summer holiday.
• They paid their fines, gave some interviews and towards the end of the summer they went on holiday.
• I hope that before the summer holiday I will be able to submit a formal motion to make their agreement binding.
• He never married, worked as an engineer for may years, and when he retired he decided to live in Araruama, a city near Rio de Janeiro. That is where the whole family went to spend the summer holidays with the children.
• Like when you change schools, or end the summer holidays.
• No matter how hard it is, you can't come home until the summer holidays.
• I can't wait for the summer holidays.
• It was on my summer holidays.
• Come and see me in Tokyo in your summer holidays.
• Come and see me in the summer holidays.
• Our aim is to present a revised proposal after the summer holiday.
• Some 200 million Europeans chose a destination with recreational water for their summer holidays.
• Not just a summer holiday or visit...
• I decided to start my summer holidays earlier.
• It's summer holidays, Mrs Rogers.
• (Gandini) here and spent the summer holidays surrounded by his friends.
• You indicated that this might be ready by August, which misses this year's summer holiday period.
• The workers suspect that the factory will be closed down after the summer holidays.
• I'll have exams right after the summer holidays.