Jails are used for summary offences and people on 'remand', i.e. those who are not let out on bail.

From: https://globalnews.ca/news/11774018/ontario-jail-capacity-figures/

New documents obtained by Global News using freedom of information laws reveal Ontario’s correctional facilities are operating at an average of 130 per cent full, with just five of the 25 facilities on the list reporting less than 100 per cent occupancy.

...

The same data from The Canadian Press found that roughly 80 per cent of all inmates at Ontario’s jails were awaiting trial — and therefore innocent under the country’s legal system.

The ad is refering to massive expansion projects at jails and building new ones like the one proposed in Kemptville. You can read about opposition to the project here: https://cappontario.ca/

I grew up in the neighborhood of the South Toronto Detention Centre. It was supposed to improve upon the former Mimico Detention Center, but they didn't staff it adequately, so lockdowns were common and the benefit of the new facilities was not given to the inmates.

That area has a long legacy of horrific practices in the name of the prison industrial complex, and you can see scars people carry from it.

The Toronto Youth Assessment Centre was on that site. It was a nightmare of a place. I wasn't criminally involved, but I was involved with the mental health care system and I was always so scared I'd be sent to a place like that if I didn't behave. After all, that was always the threat in school for kids who acted out.

It was also the site of the Victoria Industrial School. Industrial schools and industrial farms are absolutely fascinating and horrible concepts. I'll spare you the info dump, but I often think of Angela Davis's book Are Prisons Obsolete and how prisons and the carceral system was initially intended as a kind reform to how criminal behavior was dealt with. I don't think history is going to judge us kindly for building more prisons to house people in remand and then fail to staff them or care for those people.

Finally, the Lakeshore Psychiatric Hospital cemetery is very nearby. Another reminder of the fate of people society deems problematic.