@Jake Pham Congrats on the appreciation made in just 2.5 years! Seems like you made a good bet on that house.
Based on the numbers you are giving, it looks like you are going to increase your returns with the quadplex in MO for the $90,000 you have. Just keep in mind, you probably wont have $90k at your disposal after paying for prorated taxes, title fees, and other closing costs. You will be close though.
Keep in mind that you will pay 15% on the appreciation you made but you will also pay 25% on the unrecaptured depreciation that you took over the 2.5 years you owned it. Depending on Illinois tax law, you may also have state capital gains to pay also. If you haven't yet, you need to talk with a qualified intermediary to ensure you are compliant with the 1031 stipulations. They will need to hold onto the funds after you sell your property in Illinois and they also will disburse the funds when you buy the quad in MO.
If it were me, I probably would have refinanced your property in Illinois and took the cash out from the refinance to the property in MO. You had plenty of unleveraged cash flow returns in your property in IL to be able to use leverage in a positive manner and maximize your cash flow potential. However, since you are already in the process of selling, I would go ahead and talk with a qualified intermediary and do a 1031. No need to give extra money away when you can put that money to work in the nice cash flowing property in MO.
If for some reason the property sale in IL falls apart, really think about the refinance options. You might have already given it thought but the numbers really would make sense in your situation.
James Storey, CCIM