I've had this juniper for about two and a half years. I think around spring I noticed it was a little brown. Then through the summer it got worse. I thought maybe the combination of heat and little rain was the culprit. But we've had a lot of rain over the past month or so and it's not looking any better. Any idea whats going on?

If it has been declining for a while due to heat and insufficient water, it will not be a quick recovery.
I suspect that it hasn't been watered properly for 4, maybe 6 months. Since you didn't provide much information, such as climate zone, exposure, such as west, east, north or south, temperature extremes, how often do you water, fertilize, etc. , there isn't much for the people here to go on.
The more you provide us, the better our answer can be.
But regardless, what takes months to develop is not cured in a month.

Ok thanks. I'm in New Mexico. It's on a drip line. Think it's set to 15 minutes three days a week. It faces east. Mild winters and not too hot summers. It gets below freezing a handful of times in the winter but usually warms up by noon. Snow hardly ever sticks. Summers are usually in the 90s.

You have really got to water these things in the heat of summer. You have to get water down to the entire root mass. It is doubtful in my mind that the 15 minutes on a drip line accomplish that.

I think of it as a bank. If you start out with a dollar in your account and you deposit 10 cents a week, you will slowly build the account up. But if "the weather" is withdrawing 25 cents a week, your account will be over drawn in no time.
Try really giving it a good soaking at least once every week, maybe twice during the warm weather. There aren't many plants that enjoy 90 degrees! Perhaps a little nitrogen in the spring will help? Use a water soluble fertilizer at 1 tsp. per gallon. Then see if it doesn't perk up a bit. Just don't over fertilize it! Fertilizer supports good growth, it does not create good growth.

Ok thanks. I'll give that a try. Before we planted it, we had a much larger juniper in the same location. It did fine with the drip line, but maybe because it had more established roots.

Also, I'm not sure if this might be related, but we did stucco just before we planted this one. Not sure if there could be any runoff from the stucco contaminating the soil.

I doubt it is because of the stucco.
I think it is doing poorly because of not enough water. Evergreens are especially susceptible to drying out and browning because they have foliage or needles year round. They can lose a lot of moisture that way due to evaporation.

I gave it a good soak and used some Jobes evergreen fertilizer spikes. Will soak it once a week and fertilize it spring and fall. Hopefully that takes care of it.

Good luck.