Quorum

As an HOA, the IL Common Interest Community Association Act applies. If you are incorporated as a nonprofit (most associations are) then Corporate law also applies.

Per 765 ILCS 160/1-40:

(1) Twenty percent of the membership shall constitute a quorum, unless the community instruments indicate a lesser amount.

Per the wording "of the membership" it would include all the lots.

So if there are 100 lots in the development (irregardless of their voting privileges) you would need 20 lots to be represented in person or by proxy to establish a quorum.

The actual number of yea votes needed to adopt or elect would depend on the language used within your governing documents.

Example:

100 lots, 70 lots allowed to vote, 40 lots represented at the meeting, 37 ballots cast with 20 yea and 17 nay votes

Quorum = 20 lots needed (20 percent of 100 lots)
2/3 of membership = 67 yea votes required to pass (2/3 of 100 lots)
2/3 of members present = 27 yea votes required to pass (2/3 of 40 lots)
2/3 of ballots cast = 25 yea votes required to pass (2/3 of 37 ballots)

majority of membership = 51 (100 lots divided by 2 plus 1)
majority of members present = 21 (20 lots divided by 2 plus 1)
majority of votes cast = 19 (37 ballots divided by 2 rounded up)

Note: majority = more than half

Hope this helps,

Tim