I haven't heard of people overwintering portulacas, although I don't see any reason why you wouldn't be able to.
The main reason for this is that portulacas are extremely easy to grow from seed and grow very well in the northern US, where you are.
So I really wouldn't worry about overwintering it and would simply leave it in the ground and start afresh in spring.
gardening.stackexchange.com/users/109/Lorem Ipsum
Portulaca grandiflora (assuming this is what you're talking about) is an annual, so it seems unlikely that overwintering indoors will work.
They reproduce via seed.
You may be able to extend the season long enough for it to flower and set seed while you have it potted indoors.
Then you could collect seed and replant outside next spring.
I would note that the seed is fairly cheap (I see 5000 seeds online for $8; you can probably find end-of-season packets in the discount rack right now for $0.99 or less), so it may be best to just buy seed and replant in the spring.
gardening.stackexchange.com/users/51/bstpierre
I have a beautiful window box of portulaca growing right now
that came up from the plants that I never dug out last year!
It was quite a surprise, but they must have gone to seed and wintered well outside.
Of course the plants that came up were not in any orderly fashion, so when they got large enough, I dug up the plant plugs and replanted them in a tidier way.
It looks great now.
Best box I've ever had.
I only have a handful of blooms so far, but heaps of buds ready to pop!
gardening.stackexchange.com/users/5774/Karin
This is one of my fav
’s
I pluck the dead flowers off and find the seed pod .
Dust the tiny seeds on a paper plate and save them in a paper bag for next year .
During the Season I put the part I plucked just 1/2 inc into any dirt and it also grows more plants this plant is amazing
gardening.stackexchange.com/users/24009/Kelly
My aunt does it very year.
She brings some in and puts them in an upstairs window.
They root easily and she breaks off pieces and uses these as starters in spring.
gardening.stackexchange.com/users/26551/Felicia E Byrum
I have been able to overwinter portulacas in our sunroom, where they get good light all winter.
gardening.stackexchange.com/users/25480/Adam Myers
My  portulaca  is growing a clump of short stems at the base of the plant like a  sedum . The sedums use this to grow the next years growth. Could I dig my portulaca up and overwinter it indoors?  Update:  The plant did overwinter and grew well the entire next season. However, It didn't produce seed.
Can portulacas be overwintered indoors?
gardening.stackexchange.com
<plant-health><transplanting><overwintering>
gardening.stackexchange.com/questions/2575
gardening.stackexchange.com/users/419/J. Musser
I wouldn't worry about overwintering it and would leave it in the ground to start again next spring. However, you could extend the season by bringing it indoors. Rather than worry about overwintering you could simply leave it in the ground and start afresh in spring. Portulaca grandiflora is an annual, so it seems unlikely that overwintering indoors will work, but you may be able to extend the season long enough for it to flower and set seed while you have it potted indoors.
Rather than worry about overwintering you could simply leave it in the ground and start afresh in spring. Portulaca grandiflora is an annual, so it seems unlikely that overwintering indoors will work, but you may be able to extend the season long enough for it to flower and set seed while you have it potted indoors.