Сто людей у парку.

Because after сто (one hundred), Ukrainian uses the genitive plural form of the noun.

• люди = people (basic dictionary/plural form)
• людей = of people / people after many numerals

So:

• сто людей = one hundred people
• not сто люди

This is a very common pattern with larger numbers in Ukrainian.

The basic form is люди (people).

людей is a different case form of the same noun. The noun людина means person, and its plural is люди. Its genitive plural form is людей.

So the forms are:

• singular: людина = person
• plural: люди = people
• genitive plural: людей

In the present tense, Ukrainian usually does not use a verb equivalent to English are/is/am in simple sentences like this.

So:

• Сто людей у парку. literally looks like One hundred people in the park.
• But it means There are one hundred people in the park or One hundred people are in the park.

This is completely normal in Ukrainian.

У парку means in the park. Here:

• у = in
• парку = park in the locative case

After у / в when talking about location, Ukrainian usually uses the locative:

• у парку = in the park
• у місті = in the city
• у школі = in the school

The basic form is парк, but after у for location it becomes парку.

Both у and в can mean in. Ukrainian often chooses between them for easier pronunciation and smoother sound.

So у парку and в парку can both be possible in principle, but у парку is very natural here.

This choice often depends on the sounds around the word rather than a difference in meaning.

Yes, Ukrainian word order is more flexible than English word order.

Сто людей у парку. is a neutral, natural sentence meaning There are one hundred people in the park.

You may also hear:

• У парку сто людей.

This puts a little more focus on the park as the setting: In the park, there are one hundred people.

Both are grammatical. Word order in Ukrainian often changes focus or emphasis, not the core meaning.

A simple approximate pronunciation is:

sto lyu-DEY oo PAR-koo

A few notes:

• сто = sto
• людей sounds roughly like lyu-DEY
• у = oo
• парку = PAR-koo

The stressed syllables are typically:

• сто
• люде́й
• па́рку

Usually сто людей means exactly one hundred people.

If you want to sound more approximate, Ukrainian often adds words like:

• близько ста людей = about a hundred people
• десь сто людей = around a hundred people
• майже сто людей = almost a hundred people

Without such words, the default meaning is the exact number.

Yes. In natural English, these are all good translations:

• There are one hundred people in the park.
• There are a hundred people in the park.
• One hundred people are in the park.

The first two are the most natural in everyday English. The Ukrainian sentence can match any of them depending on context.

Yes. The usual everyday word here is людей from людина / люди. That is the normal choice for people in this kind of sentence.

A more formal option would involve особа (person), for example:

• сто осіб = one hundred persons

But сто людей is much more common in ordinary speech.