Are there multiple strongholds with end portals or just one?

Default Minecraft world generates three "end dungeons" (strongholds), about 1000 blocks from the centre of the world, spread equally. That means that when you're standing at X/Z 0,0 coordinates and looking in the direction of one, the other two will be at 120° to the left and to the right. All of them have a portal to the End. The Eye of Ender, when thrown, points to the closest one.

From the 1.9 version on, there are no longer just 3 strongholds.

They are now 128 per world, distributed in 8 rings (see the link above for how many generate per each ring). Their distribution is:

• The First (1st) ring with 3 strongholds ranging from 1408 to 2688 blocks away from origin.
• The Second (2nd) ring with 6 strongholds ranging from 4480 to 5760 blocks away from origin.
• The Third (3rd) ring with 10 strongholds ranging from 7552 to 8832 blocks away from origin.
• The Fourth (4th) ring with 15 strongholds ranging from 10624 to 11904 blocks away from origin.
• The Fifth (5th) ring with 21 strongholds ranging from 13696 to 14976 blocks away from origin.
• The Sixth (6th) ring with 28 strongholds ranging from 16768 to 18048 blocks away from origin.
• The Seventh (7th) ring with 36 strongholds ranging from 19840 to 21120 blocks away from origin.
• The Eight (8th) ring with 9 strongholds ranging from 22912 to 24192 block away from the origin.