The Benham Trail is an alternative to the Bill Williams Trail. I prefer it to the Bill Williams as it actually has some views along it's length and not just at the top. The trail is on the eastern and southern slope of the mountain so it is warmer and drier than the Bill Williams Trail. It is 9 miles round trip and 2035 feet up to the summit from the trailhead.
Unlike the Bill Williams Trail, this trail has a view to the south. Because of that you can see a storm developing and can turn back if the weather looks like it is going to get bad. This can be helpful in monsoon season, and from personal experience I can tell you that the lack of a view in the valley that the Bill Williams Trail climbs in can be bad. I have been caught on the summit waiting out a rough storm, which I couldn't see blowing up from the southeast while I was hiking in the narrow, densely forested valley.
From Williams, find 4th Street, or County Road 73 which is locally called Perkinsville Rd, and go south. In Williams, it is signed as "4th St" and it is just west of the tourist trap which is downtown. BTW, you can tell Californians enter the Grand Canyon from Williams because it is the only town in Arizona which I have observed to have Pizza Factory. Drive south on 4th St/ Rt 73/ Perkinsville Rd for roughly 3.5 mile to Forest Road 140. Do not turn onto the road that goes to the local ski area as that is not the correct road. At FR 140, there is a sign for the Benham trailhead. Turn right (west) and drive the rough but paved road 0.3 miles to the parking area. The trailhead has a pit toilet and a pick-nick table. The trail begins through a horse gate (you'll see if you go there). For this lightly used local trail, parking is ample, day or night, but you will not encounter anyone shouting, "howdy neighbor!". There is passenger vehicle parking and horse trailer parking.
The trail begins in ponderosa pine, some of which burned in a recent fire, and continues through pretty old ponderosa for most of the hike. There are areas of healthy gambel oak and some aspen up higher. Vegetation on the trail is lush for the dry southern exposure and this is evidence of the wet nature of Bill Williams Mountain when it is receiving precipitation. The relatively deep Dacite based soil also seems to hold water within it for a while. The trail was built in the 1920s for horses, so it is smooth and has a gentle grade for it's length.
While you will cross the road a number of times, once near the summit you have to hike on it for the last 0.25 miles or so. This is the same as the Bill Williams Trail. It isn't bad, and there are some nice yellow columbines that grow along it near the summit. Most of the time the summit fire tower is open to the public. If not, there are other good views to be had from around the summit.
The trail is multi-use, so horses and bikes may be encountered. You can ride a bike up or down the trail, and incorporate the road into a ride if you choose. The mountain access road connects to the the paved road from Williams (4th St/ RT 73/ Perkinsville Rd) just south of the trailhead turn-off (FR 140).
Plan for the weather, which includes monsoon storms in July, August and early September. Snow is normal in winter. The trail is typically dry in Autumn and most of Spring. Because Bill Williams Mt is closer to the Rim than any of the other 9000' mountains in the San Francisco Volcanic Field, it gets more snow and rain than any of them. That means the storms in summer can start earlier and be a little heavier, and the snow in winter can be very deep. However, with the southern exposure of the trail it can melt out a little faster then other aspects on the mountain. This is a hike, nothing special required to summit the hill.