Presumably you're talking about Develop presets and not Import presets; there are a difference between the two although you can apply Develop presets when importing images. Import presets are created in the Import dialog box and control the source of your images, "how" the images are linked to Lightroom's database, whether or not images are moved, converted to DNG, etc.
Your Develop presets can be organized into folders to make them easier to scroll through. Unfortunately you can't do nested folders so you're limited to one level of folders.
To organize your Develop Presets into folders; navigate to C:\Users\[User Name]\AppData\Roaming\Adobe\Lightroom\Develop Presets or equivalent path (dependent on your operating system) and add named folders. You can then drag and drop your presets into the named folders and they will show up in Lightroom's Develop Presets panel.
Here's how my presets are organized:
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However the most logical option is to resist downloading and installing presets you're unlikely to use. When I first started I downloaded every preset I could find but quickly realized that I'd never use them; so now apart from a few commercial preset packages I prefer to make my own.